DDT exposure induces tremor-like behavior and neurotoxicity in developmental stages of embryonic zebrafish

Dichlorodiphenyltrichloroethane (DDT) is a broad-spectrum insecticide, widely detected in environments due to its high stability characteristic and long natural half-life period. The adverse impact of DDT exposure on organisms and humans has attracted great concern worldwide. The current study explored the developmental and neurobehavioral toxicity response of DDT in embryonic zebrafish. The embryos were treated with DDT (0, 0.1, 1, 2.5 and 5 µM) during 6 h post fertilization (hpf) to 144 hpf. Our result indicated that DDT exposures increased the embryo hatching rate at 48 and 60 hpf, the larval malformation rate at 120 hpf and mortality rate at 144 hpf. The manifested malformations included uninflated swim bladder, bent spine and tail, deformed liver, and pericardial edema. The 120 hpf larval organs size of the gut and swim bladder was decreased in higher exposed concentration groups. Besides, DDT exposure resulted in hyperactivity for the embryo spontaneous movement at 24 hpf and tremor like movement measured by the free larval activity at 72 hpf, as well as the larval activity at 96 hpf under light-dark transition stimulus. Mechanistic examinations at 120 hpf revealed DDT exposure elevated oxidative stress through MDA formation increase, ATP level decrease as well as antioxidant enzyme genes (sod1 and gpx1a) expression decrease. DDT exposure induced abnormal neurotransmitters expression with DA level increase, 5-HT and NOS level decrease. DDT exposure suppressed the gene expressions involved in axon development (rab33a and nrxn2a) and potassium channel (kcnq2 and kcnq3). Our results suggest that the hyperactivity and tremor like movement in DDT-exposed embryos/larvae may result from oxidative stress involved with neuronal damage.

DNA methylation reprogramming mediates transgenerational diabetogenic effect induced by early-life p,p'-DDE exposure

Increasing evidence shows that an adverse environment during the early fetal development can affect the epigenetic modifications on a wide range of diabetes-related genes, leading to an increased diabetic susceptibility in adulthood or even in subsequent generations. p,p'-Dichlorodiphenoxydichloroethylene (p,p'-DDE) is a break-down product of the pesticide dichlorodiphenyltrichloroethane (DDT). p,p'-DDE has been associated with various health concerns, such as diabetogenic effect. However, the precise molecular mechanism remains unclear. In this study, p,p'-DDE was given by gavage to pregnant rat dams from gestational day (GD) 8 to GD15 to generate male germline to investiagate the transgenerational effects. We found that early-life p,p'-DDE exposure increased the transgenerational diabetic susceptibility through male germline inheritance. In utero exposure to p,p'-DDE altered the sperm DNA methylome in F1 progeny, and a significant number of those differentially methylated genes could be inherited by F2 progeny. Furthermore, early-life p,p'-DDE exposure altered DNA methylation in glucose metabolic genes Gck and G6pc in sperm and the methylation modification were also found in liver of the next generation. Our study demonstrate that DNA methylation plays a critical role in mediating transgenerational diabetogenic effect induced by early-life p,p'-DDE exposure.

Degradation of DDT by γ-hexachlorocyclohexane dehydrochlorinase LinA

1,1,1-Trichloro-2,2-bis(4-chlorophenyl)-ethane (DDT) is the first synthetic insecticide and one of the most widely used pesticides. The use of DDT has been banned, but it remains one of the most notorious environmental pollutants around the world. In this study, we found that γ-hexachlorocyclohexane (γ-HCH) dehydrochlorinase LinA from a γ-HCH-degrading bacterium, Sphingobium japonicum UT26, converts DDT to 1,1-dichloro-2,2-bis(4-chlorophenyl)-ethylene (DDE). Because of the weak DDT degradation activity of LinA, we could not detect such activity in UT26 cells expressing LinA constitutively. However, the linA-deletion mutant of UT26 harboring a plasmid for the expression of LinA, in which LinA was expressed at a higher level than UT26, showed the DDT degradation activity. This outcome highlights the potential for constructing DDT-degrading sphingomonad cells through elevated LinA expression.

Dichlorodiphenyltrichloroethane inhibits soil ammonia oxidation by altering ammonia-oxidizing archaeal and bacterial communities

Dichlorodiphenyltrichloroethane (DDT), a persistent organic pollutant, has known effects on natural microbes. However, its effects on soil ammonia-oxidizing microbes, significant contributors to soil ammoxidation, remain unexplored. To address this, we conducted a 30-day microcosm experiment to systematically study the effects of DDT contamination on soil ammonia oxidation and the communities of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). Our findings revealed that DDT inhibited soil ammonia oxidation in the early stage (0-6 days), but it gradually recovered after 16 days. The copy numbers of amoA gene of AOA decreased in all DDT-treated groups from 2 to 10 days, while that of AOB decreased from 2 to 6 days but increased from 6 to 10 days. DDT influenced the diversity and community composition of AOA but had no significant effect on AOB. Further, the dominant AOA communities comprised uncultured_ammonia-oxidizing_crenarchaeote and Nitrososphaera sp. JG1: while the abundance of the latter significantly and negatively correlated with NH 4+-N (P ≤ 0.001), DDT (0.001 < P ≤ 0.01), and DDD (0.01 < P ≤ 0.05) and positively correlated with NO3--N (P ≤ 0.001), that of the former significantly and positively correlated with DDT (P ≤ 0.001), DDD (P ≤ 0.001), and NH 4+-N (0.01 < P ≤ 0.05) and negatively correlated with NO3--N (P ≤ 0.001). Among AOB, the dominant group was the unclassified Nitrosomonadales in Proteobacteria, which showed significant negative correlation with NH 4+-N (0.01 < P ≤ 0.05) and significant positive correlation with NO3--N (0.001 < P ≤ 0.01). Notably, among AOB, only Nitrosospira sp. III7 exhibited significant negative correlations with DDE (0.001 < P ≤ 0.01), DDT (0.01 < P ≤ 0.05), and DDD (0.01 < P ≤ 0.05). These results indicate that DDT and its metabolites affect soil AOA and AOB, consequently affecting soil ammonia oxidation.

The p,p'-DDE disturbs the M1 function without affecting the M2 phenotype nor unstimulated bone marrow-derived macrophages from BALB/c mice

DDT, a persistent organic pollutant, remains affecting human health worldwide. DDT and its most persistent metabolite (p,p'-DDE) negatively affect the immune response regulation and mechanisms involved in protecting against pathogens Such metabolite decreases the capability to limit intracellular growth of Mycobacterium microti and yeast. However, the effect on unstimulated (M0) and anti-inflammatory macrophages (M2) has been evaluated scanty. Herein, we evaluated the impact of p,p'-DDE at environmentally relevant concentrations (0.125, 1.25, 2.5, and 5 µg/mL) on bone marrow-derived macrophages stimulated with IFNγ+LPS to M1 or with IL-4 +IL-13 to M2. Thus we study whether the p,p'-DDE induces M0 to a specific phenotype or modulates activation of the macrophage phenotypes and explains, at least partly, the reported effects of p,p'-DDE on the M1 function. The p,p'-DDE did not affect the cell viability of M0 or the macrophage phenotypes. In M1, the p,p'-DDE decreased NO•- production and IL-1β secretion, but increasing cellular ROS and mitochondrial O2•-, but did not alter iNOS, TNF-α, MHCII, and CD86 protein expression nor affect M2 markers arginase activity, TGF-β1, and CD206; p,p'-DDE, did not affect marker expression in M0 or M2, supporting that its effects on M1 parameters are not dependent on M0 nor M2 modulation. The decreasing of NO•- production by the p,p'-DDE without altering iNOS levels, Arginase activity, or TNF-α, but increasing cellular ROS and mitochondrial O2 suggests that p,p'-DDE interferes with the iNOS function but not with its transcription. The p,p'-DDE decreasing of IL-1β secretion, without any effect on TNF-α, suggest that an alteration of specific targets involved in IL-1β secretion may be affected and related to ROS induction. The p,p'-DDE effect on iNOS function and the IL-1β secretion process, as the NLRP3 activation, deserves further study.

Comparative in vitro and in silico study on the estrogenic effects of 2,2-bis(4-chlorophenyl)ethanol, 4,4'-dichlorobenzophenone and DDT analogs

DDT and its transformation products (DDTs) are frequently detected in environmental and biological media. Research suggests that DDT and its primary metabolites (DDD and DDE) could induce estrogenic effects by disturbing estrogen receptor (ER) pathways. However, the estrogenic effects of DDT high-order transformation products, and the exact mechanisms underlying the differences of responses in DDT and its metabolites (or transformation products) still remain unknown. Here, besides DDT, DDD and DDE, we selected two DDT high-order transformation products, 2,2-bis(4-chlorophenyl) ethanol (p,p'-DDOH) and 4,4'-dichlorobenzophenone (p,p'-DCBP). We aim to explore and reveal the relation between DDTs activity and their estrogenic effects by receptor binding, transcriptional activity, and ER-mediated pathways. Fluorescence assays showed that the tested 8 DDTs bound to the two isoforms (ERα and ERβ) of ER directly. Among them, p,p'-DDOH exhibited the highest binding affinity, with IC₅₀ values of 0.43 μM and 0.97 μM to ERα and ERβ, respectively. Eight DDTs showed different agonistic activity toward ER pathways, with p,p'-DDOH exhibiting the strongest potency. In silico studies revealed that the eight DDTs bound to either ERα or ERβ in a similar manner to 17β-estradiol, in which specific polar and non-polar interactions and water-mediated hydrogen bonds were involved. Furthermore, we found that 8 DDTs (0.0008-5 μM) showed distinct pro-proliferative effects on MCF-7 cells in an ER-dependent manner. Overall, our results revealed not only for the first time the estrogenic effects of two DDT high-order transformation products by acting on ER-mediated pathways, but also the molecular basis for differential activity of 8 DDTs.

Effects of endocrine disruptors on the electrical activity of leptin receptor neurons in the dorsomedial hypothalamus and anxiety-like behavior in male mice

There is increasing concern about the effects of endocrine disrupting chemicals (EDCs) on human health. Recently, some EDCs are suggested to affect energy metabolism leading to increased risk of obesity. Obesogenic effects of some EDCs on adipogenesis have been reported, however, there is no study examining their potential actions on the brain circuits controlling feeding and metabolism. We have investigated effects of tributyltin (TBT) and dichlorodiphenyltrichloroethane (p,p'-DDT) on electrical activity on dorsomedial hypothalamic leptin receptor neurons (DMH^LepR), morphological adaptations in neuronal anatomy of DMH^LepR, locomotion, and anxiety-like behaviors in mice. Twenty-three Lep-Cre transgenic mice were intracranially injected with GFP virus. Control animals received intraperitoneal corn oil alone while group 2 and 3 received TBT (25 μg/kg) and p,p'-DDT (2 mg/kg) for one month. Locomotor activity and anxiety-like behavior of the animals were determined by open field test. Electrophysiological effects of TBT and p,p'-DDT on DMH^LepR neurons were determined by patch clamp method. Neuronal anatomy was determined by confocal microscopy. Spontaneous firing frequency of DMH^LepR neurons of TBT group of mice was significantly higher than both p,p'-DDT and control groups (p < 0.01). TBT and p,p'-DDT significantly decreased frequency of the spontaneous inhibitory post-synaptic currents to DMH^LepR neurons compared to the control group (p < 0.05). The time spent in the center and the number of entrances to the center by the TBT-administered mice were significantly lower than other groups (p < 0.01). The total distance traveled and mean speed of the control group of mice were significantly higher than the p,p'-DDT- and TBT-administered animals (p < 0.0001). c-Fos activity of the p,p'-DDT- and TBT-administered animals were significantly elevated compared to the control group (p < 0.001), while no change in the number of dendritic spines were observed. In conclusion, this study demonstrates that exposure to TBT and p,p'-DDT alters electrical activity in DMH^LepR neurons and behavioral state in mice.

Investigation of obesogenic effects of hexachlorobenzene, DDT and DDE in male rats

Obesity has become a very important public health problem and is increasing globally. Genetics, individual and environmental factors play roles in the etiology of this complex disorder. Recently, several environmental pollutants have been suggested to have obesogenic activities. Peroxisome proliferator activating receptor gamma (PPARγ), uncoupling protein-1 (UCP1) and their expression in white adipose tissue (WAT) and brown adipose tissue (BAT) play key roles in adipogenesis. UCP3 and irisin were reported to play roles in non-shivering thermogenesis. Our primary aim was to investigate obesogenic effects of hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) in rats. In addition, thermoregulatory effects of HCB, DDT and DDE were also investigated by analyzing the levels of Ucp3 and irisin. Thirty-two adult male Sprague-Dawley rats were randomly divided into four groups as control, HCB, DDT and DDE. Animals were administered with organochlorine pesticides (OCPs; 5 mg/kg bw) by oral gavage every other day for five weeks. At the end of the experimental period, the animals were sacrificed, BAT and WAT samples were collected to analyze Pparγ, Ucp1 and Ucp3 levels. Moreover, skeletal muscle samples were collected to examine Ucp3 and irisin levels. Serum glucose, cholesterol and triglyceride levels were also determined. Body weight and core temperature of the animals were not significantly affected by any of the OCP administration. Serum glucose, cholesterol and triglyceride levels were similar among the experimental groups. Pparγ expression was significantly elevated by HCB administration only in WAT (p < 0.05). On the other hand, both Pparγ and Ucp1 expressions were diminished in WAT and BAT (p < 0.01) by DDT treatment, while in WAT, DDE significantly decreased Pparγ expression without altering its expression in BAT (p < 0.001). Ucp3 and irisin levels in skeletal muscle were not altered. Our findings show that both DDT and DDE reduce the browning of WAT by suppressing white adipocytes and thus may have obesogenic activity in male rats without altering thermoregulation. In addition, HCB, DDT and DDE-induced alterations in expression of Pparγ and Ucp1 in WAT implicates differential regulation of adipogenic processes.

Evaluations of two glutathione S-transferase epsilon genes for their contributions to metabolism of three selected insecticides in Locusta migratoria

The insect-specific epsilon class of glutathione S-transferases (GSTEs) plays important roles in insecticide detoxification in insects. In our previous work, five GSTEs were identified in Locusta migratoria, and two recombinant GSTEs, rLmGSTE1 and rLmGSTE4, showed high catalytic activity when 1-chloro-2,4-dinitrobenzene (CDNB) was used as a substrate. In this work, we further investigated whether these two GSTEs could metabolize three insecticides including malathion, deltamethrin and DDT. Using ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC/MS) method, we found that rLmGSTE4, but not rLmGSTE1, can metabolize malathion and DDT. Malathion bioassays of L.migratoria after the expression of LmGSTE4 was suppressed by RNA interference (RNAi) showed increased insect mortality from 33.8% to 68.9%. However, no changes in mortality were observed in deltamethrin- or DDT-treated L.migratoria after the expression of LmGSTE4 was suppressed by RNAi. Our results provided direct evidences that LmGSTE4 participates in malathion detoxification in L.migratoria. These findings are important for understanding the mechanisms of insecticide resistance in L.migratoria and developing new strategies for managing the insect populations in the field.

Influence of Dietary Lipid Type on the Bioavailability of DDT and Its Metabolites in Soil: Mechanisms and Health Implications

The impact of dietary lipid type on DDTr (DDT and its metabolites) relative bioavailability (RBA) in soil was investigated using an in vivo mouse model and in vitro assays. Three different lipids were long chain triglycerides (LCT), medium chain triglycerides (MCT), and short chain triglycerides (SCT). DDTr-RBA markedly (p < 0.05) increased from 51.3 ± 10.8% (control) to 94.6 ± 15.9% (10% w/w LCT) and 112 ± 20.8% (20% LCT) in LCT amended treatments. A significant increase in DDTr-RBA (92.2 ± 9.84%, p < 0.05) was also observed when mice were administered diets containing 20% MCT; however, no influence on DDTr-RBA was observed for SCT amended diets. Mechanism exploration showed that LCT and MCT enhanced DDTr solubilization by a factor of 7.31-9.59 compared to controls as a consequence of micelle formation which promoted DDTr mobilization from soil. LCT significantly enhanced DDTr intestinal absorption via increasing synthesis and secretion of apolipoprotein B 48 (32.2 ± 2.08 mg/L), compared to MCT (22.1 ± 1.32 mg/L) and SCT (15.5 ± 2.03 mg/L) treated Caco-2 cells. Mouse gut microflora analysis highlighted that LCT and MCT may increase intestinal permeability by regulating abundance of Lactobacillus, which may influence the absorption of DDTr.

Assessment of DDT and its Metabolites Bioaccessibility in Historically Contaminated Soils Using Unfed and Fed in Vitro Methods

Bioaccessibility of hydrophobic organic contaminants (HOCs) from unintentional ingestion of soil is increasingly assessed with in vitro gastrointestinal models incorporating a sorption sink. In this study, the bioaccessibility of DDTs in contaminated soils (n = 11) was determined using "unfed" unified bioaccessibility method (UBM) and fed organic estimation human simulation test (FOREhST) with/without Tenax as an absorbent. By adding Tenax, the bioaccessibility of DDTs determined using UBM was significantly increased from 4.9-30.6% to 31.6-86.0%. In contrast, the bioaccessibility of DDTs determined using FOREhST without/with Tenax were similar with values of 20.0-60.9% vs 31.5-47.6%, implying that the influence of food components on the absorption efficiency of the sink should not be overlooked. Much high fraction of DDTs (bioaccessibility: 11.7-24.8%) remained in FOREhST supernatant after Tenax collection, suggesting that prediction of bioavailability through bioaccessibility obtained by absorbent needs to be treated with caution when bioaccessibility is determined using a "fed state" in vitro method.

Amplification and Characterization of DDT Metabolizing Delta Class GST in Sand Fly, Phlebotomus argentipes (Diptera: Psychodidae) From Bihar, India

Phlebotomus argentipes is an established vector for Visceral leishmaniasis prevalent in the Indian subcontinent. Insect Glutathione S-transferases (GST) enzyme plays a pivotal role in the metabolism of xenobiotics and chemical insecticides. We report herein the identification and characterization of a delta class GST from the sandfly, P. argentipes. The resulting clone (rParg-GSTδ) is successfully sequenced, which revealed 76.43% and 66.32% gene identity with GST from Phlebotomus papatasi (Scopoli; Diptera: Psychodidae) and Lutzomiya longipalpis (Lutz and Neiva; Diptera: Psychodidae), respectively. The identified rParg-GST amino acid Blast results revealed 82.6% homology to delta class GST of Phlebotomus papatasi and more than 50% homology to Lepidoptera which comprises butterflies and moths. The Phylogenetic analysis of Parg-GST with different classes of Insect GSTs further supported its classification as delta class. A functional recombinant Parg-GSTδ protein (rParg-GSTδ) was expressed in Escherichia coli (Migula; Enterobacterales: Enterobacteriaceae) cells in a soluble form, purified to homogeneity and found to be active against a substrate 1-chloro-2,4-dintrobenzene (CDNB) and lipid peroxidation by-product 4-Hydrxynonenal (4-HNE). Interestingly, rParg-GSTδ demonstrates high dehydrochlorination activity against dichlorodiphenyltrichloroethane (DDT) i.e., 16.27 nM/µg in high performance liquid chromatography (HPLC) assay. These results provide evidence of direct DDT metabolism property exhibited by P. argentipes GST and set the foundation to decipher the metabolic resistance mechanism in P. argentipes against insecticides.

Neurobehavioral anomalies in zebrafish after sequential exposures to DDT and chlorpyrifos in adulthood: Do multiple exposures interact?

A sequence of different classes of synthetic insecticides have been used over the past 70 years. Over this period, the widely-used organochlorines were eventually replaced by organophosphates, with dichlorodiphenyltrichloroethane (DDT) and chlorpyrifos (CPF) as the principal prototypes. Considerable research has characterized the risks of DDT and CPF individually, but little is known about the toxicology of transitioning from one class of insecticides to another, as has been commonplace for agricultural and pest control workers. This study used adult zebrafish to investigate neurobehavioral toxicity following 5-week chronic exposure to either DDT or CPF, to or their sequential exposure (DDT for 5 weeks followed by CPF for 5 weeks). At the end of the exposure period, a subset of fish were analyzed for brain cholinesterase activity. Behavioral effects were initially assessed one week following the end of the CPF exposure and again at 14 months of age using a behavioral test battery covering sensorimotor responses, anxiety-like functions, predator avoidance and social attraction. Adult insecticide exposures, individually or sequentially, were found to modulate multiple behavioral features, including startle responsivity, social approach, predator avoidance, locomotor activity and novel location recognition and avoidance. Locomotor activity and startle responsivity were each impacted to a greater degree by the sequential exposures than by individual compounds, with the latter being pronounced at the early (1-week post exposure) time point, but not 3-4 months later in aging. Social approach responses were similarly impaired by the sequential exposure as by CPF-alone at the aging time point. Fleeing responses in the predator test showed flee-enhancing effects of both compounds individually versus controls, and no additive impact of the two following sequential exposure. Each compound was also associated with changes in recognition or avoidance patterns in a novel place recognition task in late adulthood, but sequential exposures did not enhance these phenotypes. The potential for chemical x chemical interactions did not appear related to changes in CPF metabolism to the active oxon, as prior DDT exposure did not affect the cholinesterase inhibition resulting from CPF. This study shows that the effects of chronic adult insecticide exposures may be relevant to behavioral health initially and much later in life, and that the effects of sequential exposures may be unpredictable based on their constituent exposures.

Investigation of steatosis profiles induced by pesticides using liver organ-on-chip model and omics analysis

Several studies have reported a correlation between pesticides exposure and metabolic disorders. Dichlorodiphenyltrichloroethane (DDT) and permethrin (PMT), two pesticides highly prevalent in the environment, have been associated to dysregulation of liver lipids and glucose metabolisms and non-alcoholic fatty liver disease (NAFLD). However, the effects of DDT/PMT mixtures and mechanisms mediating their action remain unclear. Here, we used multi-omic to investigate the liver damage induced by DDT, PMT and their mixture in rat liver organ-on-chip. Organ-on-chip allow the reproduction of in vivo-like micro-environment. Two concentrations, 15 and 150 μM, were used to expose the hepatocytes for 24 h under perfusion. The transcriptome and metabolome analysis suggested a dose-dependent effect for all conditions, with a profile close to control for pesticides low-doses. The comparison between control and high-doses detected 266/24, 256/24 and 1349/30 genes/metabolites differentially expressed for DDT150, PMT150 and Mix150 (DDT150/PMT150). Transcriptome modulation reflected liver inflammation, steatosis, necrosis, PPAR signaling and fatty acid metabolism. The metabolome analysis highlighted common signature of three treatments including lipid and carbohydrates production, and a decrease in amino acids and krebs cycle intermediates. Our study illustrates the potential of organ-on-chip coupled to multi-omics for toxicological studies and provides new tools for chemical risk assessment.

Estimated postnatal p,p'-DDT and p,p'-DDE levels and body mass index at 42 months of age in a longitudinal study of Japanese children

BACKGROUND

Children are exposed to p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT) and p,p'-dichlorodiphenyldichloroethylene (p,p'-DDE) through placental and lactational transfer. Some studies have suggested that early-life exposure to these compounds could lead to increased body mass index (BMI) during childhood. Our aim was to assess whether children's exposure during the first 2 years of life is associated with BMI z-score in Japanese children at 42 months of age.

METHODS

We used data from a birth cohort (n = 290) of the Tohoku Study of Child Development. p,p'-DDT and p,p'-DDE levels were measured in breast milk samples collected 1 month after birth, and levels in children were estimated using a toxicokinetic model for three exposure periods (0-6 months, 6-12 months, 12-24 months). Associations between exposure estimates and BMI z-score at 42 months of age were assessed using multivariate linear regression models.

RESULTS

We found no significant association between levels of p,p'-DDT measured in breast milk or estimated in children and BMI z-score. However, we observed associations between estimated p,p'-DDE levels in girls during all postnatal exposure periods and BMI z-score; for each log increase in the estimated p,p'-DDE levels, BMI z-score increased by 0.23 (C.I. 95%: 0.01, 0.45) for the 0-6 months exposure period, 0.26 (C.I. 95%: 0.06, 0.47) for the 6-12 months exposure period, and 0.24 (C.I. 95%: 0.05, 0.43) for the 12-24 months exposure period.

CONCLUSION

In this study of Japanese children, estimated postnatal p,p'-DDE levels were associated with increased BMI z-score at 42 months of age, mostly in girls. These results are in line with previous studies supporting that early-life exposure to p,p'-DDE may be associated with higher BMI during childhood.

Geographical distribution and risk assessment of dichlorodiphenyltrichloroethane and its metabolites in Perna viridis mussels from the northern coast of the South China Sea

Mussels (Perna viridis) were collected from the northern coast of the South China Sea (NSCS) to investigate the geographical distribution and potential risk of dichlorodiphenyltrichloroethane and its metabolites (DDTs). DDTs had concentrations that ranged from 248 ng/g to 4650 ng/g lipid weight (lw), with an average of 807 ± 932 ng/ng lw. A comparison of the levels of DDTs in mussels indicated that the NSCS is still one of the most polluted areas in the world, although a decreasing trend was observed. DDT metabolites were predominant in all samples, suggesting that historical residue was the main source of DDT pollution. However, there were new inputs of DDTs which likely associated with antifouling paints. The human health risk assessment revealed that the current concentrations of DDTs in mussels might pose little health risk for the consumers.

Organochlorine pesticides (HCH and DDT) in blubber of spotted seals (Phoca largha) from the western Sea of Japan

In 2014-2019, a total of 31 blubber samples were collected from spotted seals (Phoca largha) in the western Sea of Japan. The samples were analyzed by gas chromatography to determine level of organochlorine pesticides (OCPs). The concentration of hexachlorocyclohexane and its isomers (∑HCH) ranged from 389 to 50,070 ng/g lipid weght; the concentration of dichlorodiphenyltrichloroethane and its metabolites (∑DDT), ranged from 62,720 to 1,110,930 ng/g lipid wt. Transfer of HCH and DDT from mother to pup during pregnancy and lactation was documented. The OCP concentration in blubber of spotted seals from the western Sea of Japan is one to two orders of magnitude higher than in spotted seals inhabiting waters off the Japan coast. Organochlorines detected in the western Sea of Japan likely come from some countries of Southeast Asia still using OCPs in the agriculture sector.

Full-Life Cycle Toxicity Assessment of Sediment-Bound DDT and Its Degradation Products on Chironomus dilutus

Because of its hydrophobicity and persistence, dichlorodiphenyltrichloroethane (DDT) is ubiquitous in sediments and poses significant risk to benthic organisms. Therefore, it is imperative to evaluate the long-term toxicity of DDT. However, limited information is available on its chronic toxicity to benthic invertebrates. Full-life cycle toxicity of sediment-bound DDT to Chironomus dilutus was assessed. Median lethal concentrations (with 95% confidence limits) of DDT and its degradation products (DDX) to C. dilutus were 334 (165-568), 21.4 (11.2-34.3), and 7.50 (4.61-10.6) nmol/g organic carbon after 10-, 20-, and 63-d exposure, respectively. In addition, median effect concentrations of DDX were 20.0 (15.0-25.3), 7.13 (4.10-10.5), and 8.92 (3.32-15.1) nmol/g organic carbon for growth, emergence, and reproduction, respectively. A toxicity spectrum was established to visually summarize chronic effects of DDX to midges. In addition, DDT degraded to dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE) during sediment aging, and their toxicity differed from that of the parent compound. Predicted toxic units of DDX in porewater were utilized to distinguish between toxicity from DDT and that of DDD and DDE. The results showed that DDD was the main contributor to the toxicity in C. dilutus. To improve the accuracy of sediment risk assessment of DDT, the composition of DDX should be considered. Environ Toxicol Chem 2019;38:2698-2707. © 2019 SETAC.

Concentrations of organohalogens (PCBs, DDTs, PBDEs) in hunted and stranded Northern sea otters (Enhydra lutris kenyoni) in Alaska from 1992 to 2010: Links to pathology and feeding ecology

Many organohalogen compounds (OHCs) are persistent organic pollutants (POPs) found in appreciable concentrations in marine predators. While production of some POPs has declined or ceased in recent decades, their capacity for global transport and bioaccumulation results in observations of unchanging or increasing concentrations in marine systems. Sea otters (Enhydra lutris) have been advocated as an environmental sentinel for contaminants due to their longevity, site fidelity and prey species that often overlap with human consumption. Using archived (1992-2010) samples of livers from Northern sea otters (n = 50) from Alaska we examine concentrations of chlordanes (CHLs), polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDTs), and polybrominated diphenyl ethers (PBDEs) and associated metabolites. We found some evidence for declining ΣPCBs over the two decades, however for most animals concentrations were low compared to toxicological thresholds. Six animals had relatively high concentrations of ΣPCBs (mean = 262,000 ng/g lipid weight), ΣDDTs (mean = 8,800 ng/g lw), and ΣPBDEs (mean = 4,600 ng/g lw), with four of these six animals experiencing hepatic parasitism or hepatitis. In order to assess whether differences in POP concentrations are associated with feeding ecology, we examined stable isotopes of C and N in archived muscle and whisker samples. In general, there were no significant relationships between ΣPOP concentrations and stable isotope ratios. There were small differences in stable isotope profiles in animals with high POP concentrations, although it was unclear if these differences were due to feeding ecology or disease processes. This study highlights the importance of considering feeding ecology and necropsy (health and disease status) data while conducting contaminant surveys, and confirms some previous reports of trends in OHCs in Alaska marine mammals.

Evaluating toxicity risk in sediments after remediation at a Superfund megasite using a Triad approach

The Pine River downstream of the Velsicol Superfund site has been contaminated with various hydrophobic organic pollutants for more than 50 years. Remediation and sediment dredging near the site began in spring of 1999, and was completed in 2006. In 2011, the Michigan Department of Environmental Quality completed a baseline assessment report long-term monitoring plan for the Pine River. However, there has been limited assessment of the benthic community since this evaluation. The objective of this research was to evaluate the risk of Pine River sediment to aquatic macroinvertebrates downstream from the Superfund site after decades of degradation and dredging using the Triad approach. Three sites were selected downstream from the Superfund site, and an upstream reference site was used. At each site, macroinvertebrates surveys were conducted and sediments were collected for chemical analysis of DDT (1,1,1-trichloro-2,2-bis (4-chlorophenyl) ethane) and its degradation products and for laboratory toxicity testing for mortality and sublethal effects using Hyalella azteca and Chironomus dilutus. Sediment concentrations of DDT, DDD, and DDE were below levels expected to cause toxicity, and there was no observed toxicity in laboratory tests. Additionally, there were no statistically significant differences in richness, richness of Ephemeroptera, Plecoptera, and Trichoptera (EPT) species, total EPT abundance, percent EPT, or percent dominant taxa between the reference site and the downstream sites. There was an observed decrease in abundance of macroinvertebrate taxa at all downstream sites and a shift in macroinvertebrate structure when comparing the reference with most impaired sites. Although the sites downstream of the Superfund site remain different than the upstream control, there are improvements in species composition and abundance. However, more research is needed to evaluate the potential effects on ecosystem function.

Degradation of DDTs in thermal desorption off-gas by pulsed corona discharge plasma

Thermal desorption has been widely employed to treat soils contaminated with chlorinated organics. The off-gas of thermal desorption must be treated to avoid secondary pollution. In this study, the treatment of DDTs in thermal desorption off-gas by pulsed corona discharge plasma was investigated. The effects of important operation parameters, including energy density, gas temperature, humidity, and O₂ content, on DDTs degradation were investigated. The main degradation products were also studied. The DDTs degradation efficiency increased with the increase in energy density, gas temperature, and O₂ content. The degradation efficiency of DDTs was achieved to 84.6% when the initial concentration, energy density, and gas flow rate were 2.0 mg/m³, 17.8 J/L, and 3.0 L/min, respectively. Maximum DDTs degradation efficiency was observed when the gas was at 5% relative humidity. The main degradation products identified were DM, phenol, benzene, acetic acid, and formic acid. It was calculated that 87% of chlorine in the degraded DDTs was converted into chloride ion.

The synergistic interaction between sulfate-reducing bacteria and pyrogenic carbonaceous matter in DDT decay

Although 1,1,1-trichloro-2,2-di(4-chlorophenyl)ethane (DDT) was banned in the United States in 1972, it is still often detected in sediments where pyrogenic carbonaceous matter (PCM) and sulfate-reducing bacteria (SRB) co-exist. In this study, we found that 70.2 ± 0.2% of DDT disappeared in the presence of SRB and graphite powder, a model PCM, after 21 days at pH 7. Our results suggest that the observed DDT decay was due to the reaction between graphite powder and the reduced sulfur species that were produced by SRB. No biofilm formation was observed on the surface of graphite powder. Rather, the activity of SRB was inhibited by the presence of graphite powder. To understand the involvement of PCM in DDT decay, electrochemical cells and batch reactor experiments with sulfur-pretreated PCM as well as direct electrochemical reduction by a potentiostat were employed. Our results suggest that polysulfide, sulfide, sulfite, and thiosulfate could all react with PCM, forming surface-bound intermediates that subsequently led to DDT decay. The reactivity of reduced sulfur species was the highest for polysulfide, followed by sulfide, sulfite, and thiosulfate.

Reduction of halocarbons to hydrocarbons by NADH models and NADH

The reduction of halocarbons by NADH models and NADH under ambient conditions is reported as a new type of reactivity pointing towards a hitherto unknown disruptive pathway for NADH/NADPH-dependent processes. The reaction was studied with the omnipresent pesticide DDT, the inhalation anesthetic halothane, and several simple halocarbons. The halide-hydride exchange represents a biochemical equivalent for the reduction of halocarbons by traditional synthetic reagents like silanes (R₃Si-H) and stannanes (R₃Sn-H). High precision thermochemical calculations (CBS-QB3) reveal the carbon-hydrogen bond dissociation energy of NADH (70.8 kcal·mol^-1) to be lower than that of stannane (SnH₄: 78.1 kcal·mol^-1), approaching that of the elusive plumbane (PbH₄: 68.9 kcal·mol^-1). The ready synthetic accessibility of NADH models, their low carbon-hydrogen bond dissociation energy, and their dehalogenation activity in the presence of air and moisture recommend these compounds as substitutes for the air-sensitive or toxic metal hydrides currently employed in synthesis.

Residues of legacy organochlorine pesticides and DDT metabolites in highly consumed fish from the polluted Guanabara Bay, Brazil: distribution and assessment of human health risk

Organochlorine (OCP) pesticides were determined in samples of sardine (Sardinella brasiliensis), whitemouth croaker (Micropogonias furnieri), and mullet (Mugil liza) from Guanabara Bay (state of Rio de Janeiro, Brazil). OCP concentrations and fish consumption were linked with acceptable daily intake values in order to assess the human health risk for the Brazilian population. The total concentrations of OCPs (Σ OCP) was 6.6 ng/g f.w., 7.5 ng/g f.w., and 2.8 ng/g f.w. for sardines, corvina, and mullet, respectively. There was a significant difference (P < 0.05) among the species related to o,p'-DDD and o,p'-DDT concentrations. Both DDT-related compounds were 5 and 76 times more abundant in sardines than in whitemouth croaker and mullet. Newly discovered DDT metabolite, o-Cl-DDMU, was frequently detected in the fish. None of the samples exceeded the maximum limits for acceptable levels of OCP residues. According to the data of average intake of Brazilian population, none of three species exceeded toxicological parameter. The investigated fishes are considered as safe for human consumption in regard to exposure of the studied OCPs. However, fish may be a intake source of OCP metabolites such as o-Cl-DDMU whose toxicity is still unknown.

Occurrence of organochlorine pesticides and polychlorinated biphenyls in sediment and fish in Cau Hai lagoon of Central Vietnam: Human health risk assessment

This is the first study on polychlorinated biphenyls (PCBs) in fish from the Cau Hai lagoon, a part of the largest coastal lagoon in Southeast Asia. Seven selected PCB congeners and organochlorine pesticides in sediments and edible fish tissues were quantified by GC-MS. The sum of ICES-7 PCB and DDTs concentrations in fish species consumed regularly and of economic value were in ranges 26-43 ng g^-1 lw and 182-277 ng g^-1 lw, respectively. The ratio between the parent DDT compound and the sum of metabolites, DDE and DDD, was most of the time smaller than 1, suggesting primarily an historical contamination of the lagoon. An agglomerative hierarchical clustering indicates sites located in the north-western part of the Cau Hai lagoon were characterized by above-average concentrations of DDE and DDT. Comparing to previous data, a large decrease in ∑DDT residues can be seen over the past 20 years.

Cytokine expression and lymphocyte proliferative capacity in diseased harbor porpoises (Phocoena phocoena) - Biomarkers for health assessment in wildlife cetaceans

Harbor porpoises (Phocoena phocoena) in the North and Baltic Seas are exposed to anthropogenic influences including acoustic stress and environmental contaminants. In order to evaluate immune responses in healthy and diseased harbor porpoise cells, cytokine expression analyses and lymphocyte proliferation assays, together with toxicological analyses were performed in stranded and bycaught animals as well as in animals kept in permanent human care. Severely diseased harbor porpoises showed a reduced proliferative capacity of peripheral blood lymphocytes together with diminished transcription of transforming growth factor-β and tumor necrosis factor-α compared to healthy controls. Toxicological analyses revealed accumulation of polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyltrichloroethane (DDT) in harbor porpoise blood samples. Correlation analyses between blood organochlorine levels and immune parameters revealed no direct effects of xenobiotics upon lymphocyte proliferation or cytokine transcription, respectively. Results reveal an impaired function of peripheral blood leukocytes in severely diseased harbor porpoises, indicating immune exhaustion and increased disease susceptibility.

Bioaccumulation of dichlorodiphenyltrichloroethanes (DDTs) in carp in a water/sediment microcosm: important role of sediment particulate matter and bioturbation

Sediments are reservoirs and sources of DDTs to the aquatic ecosystem. However, the role of sediment particulate matter and benthic organisms in transferring DDTs remains unclear. In this study, microcosms were built up with different groups to simulate a freshwater system with DDT-contaminated sediment and organisms. The impacts of different exposure routes (water and sediment) on the changes of DDT and its metabolites (DDD and DDE) in carp (Cyprinus carpio) were investigated. The bioturbation of Tubifex tubifex (Oligochaeta, Tubificidae) was investigated to understand the fate and transfer of DDTs in aquatic environment. For the sediment treatment, the concentrations of o,p'-DDT in carp were significantly higher than those of p,p'-DDT, and the metallothionein (MT) content decreased. The bioaccumulation of DDTs in carp via sediment particulate matter was significantly higher/faster than that via overlying water. T. tubifex and sediment particulate matter accelerate DDT bioaccumulation in carp. Selective enrichment of the (+)-o,p'-DDT and (+)-o,p'-DDD was found in carp. These results help to reduce uncertainty in ecological and health risk assessments and to better understand the risk of DDTs in the environment.

Removal of persistent DDT residues from soils by earthworms: A mechanistic study

Earthworms have been reported to enhance DDT (1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane) removal from soils, but the mechanism underlying is still poorly understood. This study therefore worked on the links between DDT transformation in drilosphere and non-drilosphere matrices and the properties of these matrices in sterile and non-sterile soil columns with and without earthworms to reveal related mechanisms. The results show that earthworms shortened the half-time of DDT in soils from over 14 weeks to about 8 weeks; DDT residues were lower (p < 0.05) and its transformation products were higher (p < 0.05) in drilosphere matrixes than those in their non-drilosphere counterparts; DDD and DDMU was higher (p < 0.05) in the gut, and DDE was higher (p < 0.05) in the burrow; and the bioaccumulation of DDT in earthworm tissues only contributed less than 0.03% to the DDT removal enhanced by earthworms. The results further demonstrate that drilosphere is the hotspot of soil DDT transformation with oxidative degradation dominant in the burrow and reductive dechlorination in the gut, and earthworms enhanced DDT removal mainly by digesting and promoting the microbial degradation of DDT by indigenous microorganisms via improving soil properties. Knowledge of the mechanisms of DDT transformation by earthworms will support the use of earthworms in remediating DDT-contaminated soils.

First assessment of persistent organic pollutant contamination in blubber of Chilean blue whales from Isla de Chiloé, southern Chile

Persistent organic pollutants (POPs) were assessed for the first time in blue whales from the South Pacific Ocean. Concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), hexachlorobenzene (HCB) and dichlorodiphenyltrichloroethane and its main metabolites (DDTs), were determined in 40 blubber samples from 36 free-ranging individuals and one stranded, dead animal along the coast of southern Chile between 2011 and 2013. PCBs were the most abundant pollutants (2.97-975 ng/g l.w.), followed by DDTs (3.50-537 ng/g l.w.), HCB (nd-77.5 ng/g l.w.) and PBDEs (nd-33.4 ng/g l.w). There was evidence of differences between sexes, with lower loads in females potentially due to pollutants passing to calves. POP concentrations were higher in specimens sampled in 2013; yet, between-year differences were only statistically significant for HCB and PBDEs. Lower chlorinated (penta > tetra > tri) and brominated (tetra > tri) congeners were the most prevalent among PCBs and PBDEs, respectively, mostly in agreement with findings previously reported in blue and other baleen whales. The present study provides evidence of lower levels of contamination by POPs in eastern South Pacific blue whales in comparison to those reported for the Northern Hemisphere.

Temporal trends of PCBs and DDTs in Great Lakes fish compared to those in air

Regulations designed to lower the concentrations of PCBs and DDTs in the environment have been in place since the 1970s, but the levels of PCBs are still high enough to cause fish consumption advisories for Great Lakes fish. The levels of PCBs and DDTs have been tracked in these fish since about 1975, and the rates at which these age-adjusted concentrations have been decreasing over the period 1999-2014 have been recently been estimated. This paper compares these rates to ones estimated from the entire data set (~1975-2014) and to rates estimated from changes in atmospheric concentrations, which have been tracked since 1992. In general the halving times (9-17 years for PCBs and 7-10 years for DDTs) estimated from the full fish dataset are similar to those estimated from the atmospheric data, suggesting that the atmospheric and the fish levels are coupled. The more recent, age-adjusted rates are sometimes significantly faster than those from the full fish and atmospheric datasets, suggesting that the air-water dynamic may now be changing.

Persistent organic pollutants (POPs) in edible fish species from different fishing zones of Croatian Adriatic

High-risk contaminants, OCPs and PCBs, were investigated in marine fish from the Adriatic Sea, from which retail fish in Croatia is commonly sourced. The pollutant levels in sardine, horse and chub mackerel, anchovy and round sardinella were analysed based on a two-year sampling and the joint use of generally accepted statistics and advanced clustering methods - self-organizing maps (SOM) and decision tree analysis (DT). Both the SOM and DT suggested fish mass and length rather than fat along with α-HCH, p,p'-DDT, PCB-74 and PCB-189 to cause variable pollutant uptake among species. Main distinctions of sardines occur in coastal and off coast regions rather than in a particular fishing zone and they are associated with both fish characteristics, levels of γ-HCH and PCBs: -60, -105, -150, -170, and -189. The results, mutually compatible or in agreement, could be useful for the design and implementation of the abatement strategies of fish pollution.

Bone density and asymmetry are not related to DDT in House Sparrows: Insights from micro-focus X-ray computed tomography

In organisms, DDT (Dichlorodiphenyltrichloroethane) and its metabolites, DDE (Dichlorodiphenyldichloroethylene) and DDD (Dichlorobischlorophenylethane) are endocrine mimics. They can influence bone density and other bone structural features. This study was conducted on House Sparrows (Passer domesticus) caught from the Free State - and the Limpopo Provinces of South Africa (SA). The sites were chosen based on spraying patterns of DDT for malaria control or non-spraying. The bone mineral densities of the femurs as well as the lengths of the left- and right leg bones were determined using micro-focus X-ray computed tomography (μ-XCT). The concentrations of DDT and its metabolites in the liver were determined with gas-chromatography mass-spectrometry to provide baseline concentrations of DDT in the body, allowing comparison of the various groups of birds. There was no asymmetry between the lengths of the bones of the left- and the right legs. DDT concentrations in the liver did not correlate with bone lengths. In addition, there were no significant differences between the relative densities of the left- and right leg bones with increase of concentrations of DDT. The concentrations of DDT and its metabolites did not have a significant effect on the measured bone parameters of House Sparrows. It is possible that the concentrations of DDT and its metabolites in the environments were too low to be injurious to the birds and/or tolerance to the insecticide has developed in the birds over more than six decades of almost continuous application of DDT.

Potential association between exposure to legacy persistent organic pollutants and parasitic body burdens in Indo-Pacific finless porpoises from the Pearl River Estuary, China

A high prevalence of infectious diseases (mostly lungworms) is found in finless porpoises (genus Neophocaena) in the coastal waters of China, which is one of the most dichlorodiphenyltrichloroethane (DDT)-polluted areas worldwide, while its association with contaminant exposure remains undetermined. To address this gap, we investigated blubber levels of polychlorinated diphenyls (PCBs), organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons in Indo-Pacific finless porpoises (Neophocaena phocaenoides) stranded in the Pearl River Estuary (PRE) of China. In the post-mortem examinations, lungworms (Halocercus species) were found to be the most common parasites, with a high density observed in lungs and bronchi. Severe infections by nematode parasites were also found in the uterus (Cystidicola species), intestine (Anisakis typica) and muscle (A. typica). For all the pollutant compounds analyzed, only the concentrations of p,p'-DDT, p,p'-dichlorodiphenyldichloroethane (DDD) and o,p'-DDD were significantly higher in porpoises died of infectious diseases than in the "healthy" individuals (died from physical trauma). Contrasted accumulation pattern of DDTs and their metabolites was found between animals with different health status. The proportion of p,p'-DDT in ΣDDTs was higher than that of p,p'-dichlorodiphenyldichloroethylene (DDE) in diseased animals, whereas an opposite pattern was shown for "healthy" ones. While this study is the first to describe a significant positive correlation between parasitic diseases and high levels of DDTs in cetaceans, the direction of causality cannot be determined in our data: either a parasitic infection affected the porpoises' ability to metabolize DDTs, resulting in high levels of p,p'-DDT in their blubber, or the pollutant burden rendered them more susceptible to parasitic infection.

Combined treatment of contaminated soil with a bacterial Stenotrophomonas strain DXZ9 and ryegrass (Lolium perenne) enhances DDT and DDE remediation

Bioremediation of contaminated soils by a combinational approach using specific bacterial species together with ryegrass is a promising strategy, resulting in potentially highly efficient degradation of organic contaminants. The present study tested the combination of strain DXZ9 of Stenotrophomonas sp. with ryegrass to remove DDT and DDE contaminants from soil under natural conditions in a pot experiment. The strain DXZ9 was successfully colonized in the natural soil, resulting in removal rates of approximately 77% for DDT, 52% for DDE, and 65% for the two pollutants combined after 210 days. Treatment with ryegrass alone resulted in slightly lower removal rates (72 and 48%, respectively, 61% for both combined), while the combination of strain DXZ9 and ryegrass significantly (p < 0.05) improved the removal rates to 81% for DDT and 55% for DDE (69% for both). The half-life of the contaminants was significantly shorter in combined treatment with DXZ9 and ryegrass compared to the control. The remediation was mostly due to degradation of the contaminants, as the net uptake of DDT and DDE by the ryegrass accounted for less than 3% of the total amount in the soil. DDT is reductively dechlorinated to DDD and dehydrochlorinated to DDE in the soil; the metabolites of DDE and DDD were multiple undefined substances. The toxicity of the soil was significantly reduced as a result of the treatment. The present study demonstrates that the bioremediation of soil contaminated with DDT and DDE by means of specific bacteria combined with ryegrass is feasible.

Biodegradability and ecological safety assessment of Stenotrophomonas sp. DDT-1 in the DDT-contaminated soil

The biodegradability and ecological safety assessment of the previously isolated DDT-degrading bacterial strain Stenotrophomonas sp. DDT-1 were investigated in the DDT-contaminated soil under laboratory and field conditions. Under laboratory conditions, the degradation rates of fresh p,p'-DDT in soil were enhanced by 2.0-3.0-fold with the introduction of the strain DDT-1 compared to those of the control treatments. A similar enhancement in the dissipation of DDTs (p,p'-DDT, p,p'-DDE, p,p'-DDD, and o,p'-DDT) in the aged DDT-contaminated field plot soils resulted from the inoculation with this strain. Meanwhile, the degradation rates of DDTs increased by 2.9-5.5- and 2.8-7.6-fold in the inoculated greenhouse and open field soils, respectively, after field demonstration application of strain DDT-1 preparation. Moreover, no significant differences in the soil enzyme activity, microbial functional diversity, and bacterial community structure were observed between the inoculated and un-inoculated field soils, but several soil microbial genera exhibited some fluctuations in abundance. It is concluded that strain DDT-1 could accelerate the removal of DDTs residues in field soils, and furthermore, its inoculation was ecologically safe.

Comparative study of persistent organic pollutant (POP) (chlorinated pesticides, PCBs, and dioxins/furans) concentrations in cancer-affected human organs with those of healthy organs

The concentrations of POPs (persistent organic pollutants) including 16 compounds of OCPs, 12 dioxin-like PCBs congeners, and 17 PCDDs/Fs congeners were determined in 46 human adipose tissue samples gathered from Jordanian citizens. Thirteen adipose tissue samples of healthy people were collected from Jordan University Hospital and 33 adipose tissue samples of cancer-affected patients were collected from King Hussein Cancer Center. All samples were extracted, cleaned-up, and analyzed using GC/MS. In the healthy person's samples, among the OCP compounds, the highest concentration was found for heptachlor-oxo-epoxide (5696.71 μg/kg), while among the PCB congeners, the non-ortho PCB 126 shows the highest TEQ concentrations (5554.5 μg TEQ/kg) and among the PCDDs/Fs congeners, the highest TEQ value was found for the congener 2,3,4,7,8-PeCDFs (5.93 μg TEQ/kg). For the cancer-affected patient's samples, the highest concentration among the OCP compounds was found for o,p-DDT (638.7 μg/kg), while among the PCBs congeners, the highest TEQ value was found for the non-ortho-PCB 126 (3366.24 μg TEQ/kg) and among the PCDDs/Fs congeners, the highest TEQ value was found for the congener 1,2,3,7,8-PeCDDs (20.64 μg TEQ/kg). OCP concentration level in adipose tissue samples for healthy people was 32 times higher than for cancer patient persons, while the TEQ values for dioxin-like PCB concentrations in adipose tissue samples of healthy people was 2.2 times higher than in the samples of cancer-affected patient and the TEQ values for PCDDs/Fs in adipose tissue samples of cancer-affected patient was 3 times higher than in the samples of healthy people.

Human Health Risk from Consumption of Marine Fish Contaminated with DDT and Its Metabolites in Maputo Bay, Mozambique

Many countries with incidence of malaria, including those surrounding Maputo Bay, use dichloro-diphenyl-trichloroethane (DDT) to reduce mosquitoes. This study is the first to estimate the human health risk associated with consumption of marine fish from Maputo Bay contaminated with DDTs. The median for ∑DDTs was 3.8 ng/g ww (maximum 280.9 ng/g ww). The overall hazard ratio for samples was 1.5 at the 75th percentile concentration and 28.2 at the 95th percentile. These calculations show increased potential cancer risks due to contamination by DDTs, data which will help policy makers perform a risk-benefit analysis of DDT use in malaria control programs in the region.

Sources and transformation pathways for dichlorodiphenyltrichloroethane (DDT) and metabolites in soils from Northwest Fujian, China

Dicofol (2,2,2-trichloro-1,1-bis-(p-chlorophenyl)ethanol) found in the environment is not only a miticide originated from commercial use, but also a metabolite of dichlorodiphenyltrichloroethane (DDT), which is often overlooked. To verify the sources and transformation pathways of DDT and related metabolites in soils, we measured p,p'-(dicofol + DBP) (sum of p,p'-dicofol and 4,4'-dichlorobenzophenone), DDT and six metabolites in soils from Northwest Fujian, China. The ratios of 1,1,1-trichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl)ethane (o,p'-DDT)/1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDT) and the mass balance demonstrated that p,p'-(dicofol + DBP) predominantly originated from p,p'-DDT transformation rather than from actual dicofol application. p,p'-(dicofol + DBP) accounted for 45.0% as the primary metabolites of DDT in this study, more than 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDE) and 1,1-dichloro-2,2-bis-(p-chlorophenyl)ethane (p,p'-DDD), which might lead to large overestimations of the fresh DDT input by using the traditional ratio of (∑₂DDD + ∑₂DDE)/∑₂DDT (with all o,p'- and p,p'- isomers included). In paddy fields where the conditions alternate between aerobic (dry period) and anaerobic (wet period), both p,p'-DDD and p,p'-DDE were likely to degrade to 1-chloro-2,2-bis-(p-chlorophenyl)ethylene (p,p'-DDMU), which further transformed to 2,2-bis(p-chlorophenyl)ethylene (p,p'-DDNU). Degradation of p,p'-DDMU to p,p'-DDNU mainly occurred in waterlogged paddy soils. However, p,p'-DDNU might not transform to other higher-order metabolites in aerobic surface soils. Overall, our study confirmed p,p'-(dicofol + DBP) as metabolites of p,p'-DDT, suggested DDE and DDD were parallel precursors of DDMU, and further verified the transformation pathways of DDT in surface soils.

DDTs-induced antioxidant responses in plants and their influence on phytoremediation process

Phytoremediation is a low cost technology based on the use of plants to remove a wide range of pollutants from the environment, including the insecticide DDT. However, some pollutants are known to enhance generation of reactive oxygen species (ROS), which can generate toxic effects on plants affecting the phytoremediation efficiency. This study aims to analyze the potential use of antioxidant responses as a measure of tolerance to select plants for phytoremediation purposes. Tomato and zucchini plants were grown for 15 days in soils contaminated with DDTs (DDT + DDE + DDD). Protein content, glutathione-S-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPx) and catalase (CAT) activities were measured in plant tissues. Exposure to DDTs did not affect protein content or CAT activity in any of the species. GST, GR and GPx activity showed different responses in exposed and control tomato plants. After DDTs exposure, tomato showed increased GR and GPX activity in stems and leaves, respectively, and a decrease in the GST activity in roots. As no effects were observed in zucchini, results suggest different susceptibility and/or defense mechanisms involved after pesticide exposure. Finally, both species differed also in terms of DDTs uptake and translocation. The knowledge about antioxidant responses induced by pesticides exposure could be helpful for planning phytoremediation strategies and for the selection of tolerant species according to particular scenarios.

Reductive dehalogenation of DDT with folate models: Formation of the DDT metabolite spectrum under biomimetic conditions

The insecticide DDT is an omnipresent environmental contaminant and an ongoing toxicological concern. The recent discovery that methylenetetrahydrofolate (MTHF) models are capable of reducing a range of halocarbons to hydrocarbons under biomimetic conditions has prompted us to investigate the possible role of MTHF in the metabolism of DDT. We now report that the reaction of MTHF models with DDT produces no less than five known in vivo metabolites of DDT, namely DDD, DDE, DDMU, DBP, and DDM. The capability of the MTHF models to produce the full spectrum of known DDT dehalogenation products is strong evidence that the mechanistically obscure metabolism of DDT may involve MTHF. The findings also suggest that DDT should be capable of disrupting folate-dependent pathways.

Comparisons of field and laboratory estimates of risk of DDTs from contaminated sediments to humans that consume fish in Palos Verdes, California, USA

Calculating risk from seafood exposure to persistent organic pollutants continues to be problematic as estimates of exposure from diet require extensive monitoring of fish species and limited assessments of bioavailability from sediments where the contaminants tend to reside. Previous studies in our laboratory utilized a laboratory-based isotope dilution method (IDM) to estimate the bioavailability of DDT [1,1,1-trichloro-2, 2-bis(p-chloro-phenyl)ethane] and its metabolites from sediment to biota from a superfund site on the shelf of the Palos Verdes (PVS) Peninsula in California (USA). Using a biota-sediment accumulation factor (BSAF) derived from IDM and biomagnification factors (BMF) calculated from previous studies as well as seafood-consumption data specific to anglers in the PVS area, we estimated cancer and non-cancer risks for anglers and nursing infants representing sensitive groups. Predicted cancer risks from consumption of White croaker (Genyonemus lineatus) to the 50th and 95th percentile to all shore mode anglers were, respectively, 2×10-7 and 7×10-7, which were similar to field studies using fish concentrations of all DDT isomers and their environmental degradates (ΣDDT) from collected animals. The calculated non-cancer hazard quotient values for the 50th and 95th percentile shore mode anglers consuming White croaker from this study (0.008 and 0.023, respectively) were also of similar magnitude as those obtained from studies based on samples obtained solely from fish. For nursing infants, similar results were also observed. These results indicate that estimates of bioavailability using IDM from sediment could be used accurately to determine risk to ΣDDT in humans from fish consumption.

Intake of DDT and its metabolites through food items among reproductive age women in Bangladesh

This study was conducted to make clear the major intake route of DDT in Bangladesh people to develop strategy and policy that could lead to a reduction in body burden especially in the reproductive age women. The concentrations of several POPs (DDT, PCBs, chlordanes, HCHs, HCB, and PeCB) were quantified in food items, human breast milk and house dust collected in Bangladesh in 2011-2012. Among the POPs analyzed in this study, DDT and its metabolites (ΣDDT) showed the highest concentration. The highest median ΣDDT concentration was found in meat (1.3-1100 ng g^-1 wet weight) and house dust (30-1100 ng g^-1 dry weight), and followed by human breast milk (20-55 ng g^-1 wet weight). Estimated daily intake (EDI) was calculated using the DDT concentrations in food items. The highest intake of DDT was found in an infant and 99% of it was via breast milk feeding. DDT intake via consumption of beef accounted for 69% and 72% of that found in children and adults, respectively. The total EDI of DDT did not exceed the tolerable daily intake proposed by the WHO, but the EDI of p,p'-DDT exceeded the oral reference dose proposed by the US Environmental Protection Agency. Further research is required to clarify the reason for the high levels of DDT in beef, which seems to be the major intake route of DDT for women of reproductive age in Bangladesh.

Association between Exposure to p,p'-DDT and Its Metabolite p,p'-DDE with Obesity: Integrated Systematic Review and Meta-Analysis

BACKGROUND

The prevalence of obesity is increasing in all countries, becoming a substantial public health concern worldwide. Increasing evidence has associated obesity with persistent pollutants such as the pesticide DDT and its metabolite p,p'-DDE.

OBJECTIVES

Our objective was to systematically review the literature on the association between exposure to the pesticide DDT and its metabolites and obesity to develop hazard identification conclusions.

METHODS

We applied a systematic review-based strategy to identify and integrate evidence from epidemiological, in vivo, and in vitro studies. The evidence from prospective epidemiological studies was quantitatively synthesized by meta-analysis. We rated the body of evidence and integrated the streams of evidence to systematically develop hazard identification conclusions.

RESULTS

We identified seven epidemiological studies reporting prospective associations between exposure to p,p'-DDE and adiposity assessed by body mass index (BMI) z-score. The results from the meta-analysis revealed positive associations between exposure to p,p'-DDE and BMI z-score (β=0.13 BMI z-score (95% CI: 0.01, 0.25) per log increase of p,p'-DDE). Two studies constituted the primary in vivo evidence. Both studies reported positive associations between exposure to p,p'-DDT and increased adiposity in rodents. We identified 19 in vivo studies and 7 in vitro studies that supported the biological plausibility of the obesogenic effects of p,p'-DDT and p,p'-DDE.

CONCLUSIONS

We classified p,p'-DDT and p,p'-DDE as "presumed" to be obesogenic for humans, based on a moderate level of primary human evidence, a moderate level of primary in vivo evidence, and a moderate level of supporting evidence from in vivo and in vitro studies. https://doi.org/10.1289/EHP527.

Characterization and genome functional analysis of the DDT-degrading bacterium Ochrobactrum sp. DDT-2

A strain of Ochrobactrum sp. DDT-2 that was capable of degrading DDT as the sole carbon and energy source was isolated and sequenced, and its biodegradation characteristics and metabolism mechanism were examined. The genome sequence of the isolate DDT-2 was composed of 4,630,303bp with a GC content of 55.99% and 4454 coding genes. The degradation rate of DDT by the isolate DDT-2 increased with the increasing substrate concentration (0.1-10mg/l) and temperature (20-40°C). The degradation half-life of DDT in the presence of the isolate DDT-2 at pH7.0 was obviously shorter than those at pH5.0 and 9.0. Potential DDT degradation genes were found in the isolate DDT-2 genome by a BLASTx search against a DDT degradation genes (DDGs) database. A common biodegradation pathway of DDT was proposed based on the combined analysis of genome annotation and mass spectrometry. DDT was initially dechlorinated to form DDD and DDE. Then, it was transformed into DDMU and DDA via dechlorination and carboxylation, and it may ultimately be mineralized to carbon dioxide. The results suggested that the isolate DDT-2 could be useful for the bioremediation of DDT and its metabolite residues.

Comparative analysis of microbial communities during enrichment and isolation of DDT-degrading bacteria by culture-dependent and -independent methods

Microcosms for enrichment of DDT degrading microorganisms were monitored using culture-dependent and -independent methods. Culture dependent methods isolated several strains with DDT degradation potential, Pseudomonas species being the most frequent. One isolate, Streptomyces sp. strain D3, had a degradation rate of 77% with 20mgL^-1 of DDT after 7days incubation, D3 also had degradation rates of 75% and 30% for PCB77 (3,3',4,4'-tetrachloro biphenyl) and PCNB (pentachloronitrobenzene) respectively. Culture-independent high-throughput sequencing identified a different subset of the microbial community within the enrichment microcosms to the culture dependent method. Pseudomonas, the most frequently isolated strain, only represented the 12th most abundant operational taxonomic unit in the sequencing dataset (relative abundance 0.9%). The most frequently observed bacterial genus in the culture-independent analysis did not correspond with those recovered by culture-dependent methods. These results suggested that deep sequencing followed by a targeted isolation approach might provide an advantageous route to bioremediation studies.

Organohalogenated contaminants in plasma and eggs of rockhopper penguins: Does vitellogenin affect maternal transfer?

Although many studies have investigated organohalogenated contaminants (OHCs) in yolk, little is known about the mechanisms and timing of transfer of OHCs from the female to the egg. Vitellogenin, a yolk precursor, has been suggested to play a role in this transport. We here report for the first time the temporal changes in OHC and an index of vitellogenin concentrations in female plasma from the pre-laying period to clutch completion in free-living birds: the southern rockhopper penguin (Eudyptes chrysocome chrysocome) breeding in the Falkland/Malvinas Islands. In addition, OHC concentrations in the corresponding clutches were analysed. OHC concentrations in female plasma and in the yolk of both the first (A-) and the second (B-)eggs followed a similar pattern, with hexachlorobenzene (HCB) > Σpolychlorinated biphenyls (PCBs) > Σdichlorodiphenyltrichloroethanes (DDTs) > Σmethoxylated polybrominated diphenyl ethers (MeO-PBDEs) > Σchlordanes (CHLs) > Σpolybrominated diphenyl ethers (PBDEs) ≈ Σhexachlorocyclohexanes (HCHs). The higher concentrations of MeO-PBDEs compared to PBDEs indicate a diet containing naturally-produced MeO-PBDEs. All OHC compounds except for PBDEs increased from the pre-laying period to A-egg laying and subsequently declined from A-egg laying to B-egg laying, and female plasma vitellogenin showed the same pattern. For ΣPCBs and ΣMeO-PBDEs, we found positive correlations between female plasma during A-egg laying and both eggs, and for HCB between female plasma and A-eggs only. During pre-laying, only ΣMeO-PBDEs correlated between both eggs and female plasma, and no correlations between OHC concentrations in eggs and female plasma were found during B-egg laying, highlighting that maternal transfer of OHCs is time- and compound-specific. Finally, female vitellogenin concentrations did not significantly correlate with any OHC compounds in either female plasma or eggs, and our results therefore did not confirm the suggested role of vitellogenin in the maternal transfer of OHC molecules into their eggs.

Synthesis of the DDT metabolite 2,4-dichloro-1-[2-chloro-1-(4-chlorophenyl)ethenyl]benzene (o-Cl-DDMU) and its detection in abiotic and biotic samples

Technical dichlorodiphenyltrichloroethane (DDT) has been used worldwide as a pesticide since the beginning of the 1940s. Due to its persistence, DDT residues are still ubiquitously distributed in the environment. Photochemical UV degradation has been shown to be a potent degradation path for DDT and most of the resulting photoproducts have been identified up to now. Nevertheless, in 2012, a new DDT metabolite, most likely formed photochemically from DDE, was detected in ray liver samples from Brazil, an area which is highly contaminated with DDT. This study includes photochemical generation, chemical synthesis and isolation of this compound which was verified to consist of both cis- and trans-2,4-dichloro-1-[2-chloro-1-(4-chlorophenyl)ethenyl]benzene. Both stereoisomers were resolved by gas chromatography on a polar capillary column and detected in more than 60 biotic (e.g. marine mammals, birds, human milk) and abiotic samples (fat deposits in kitchen hoods) from different areas all over the world. The stereoisomer distribution and concentrations (0.3-3.9% relative to corresponding 1,1-dichloro-2,2-bis(p-chlorophenyl) ethane (p,p'-DDE) levels) were determined by means of the synthesized analytical standard, indicating the widespread occurrence of this compound as an additional minor metabolite of DDT.

PCBs and OCPs in human milk in Eastern Siberia, Russia: Levels, temporal trends and infant exposure assessment

The aim of our study is to investigate the spatial distribution of polychlorinated biphenyls (PCBs), hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (p,p'-DDT) and its metabolites, α- and γ-isomers of hexachlorocyclohexane (HCH) in 155 samples of human milk (HM) from Eastern Siberia (six towns and seven villages in Irkutsk Region, one village of the Republic of Buryatia and one town in Zabaikal'sk Region, Russia), and to examine the dietary and social factors influencing the human exposure to the organochlorines. The median and range of the concentration of six indicator PCBs in HM in 14 localities in Eastern Siberia (114 (19-655) ng g^-1 lipids respectively) are similar to levels in the majority of European countries. However, in one village, Onguren, the median and range of levels of six indicator PCBs (1390 (300-3725) ng g^-1 lipids) were comparable to levels measured in highly contaminated populations. The Lake Baikal seals are highly exposed to persistent organic pollutants (POPs) and could be a potential source of PCB and DDT exposure in the Onguren cohort via the consumption of the Lake Baikal seal tissue. The location of food production in areas exposed to the emissions of local POP sources can also significantly influence POP levels in HM samples from industrialized areas. Estimated daily intakes (EDI) of HCH and HCB for infants are considerably lower or close to acceptable daily intake (ADI). The EDI of total DDTs and total PCBs are higher than ADI.

Assessment of tissue-specific accumulation, elimination and toxic effects of dichlorodiphenyltrichloroethanes (DDTs) in carp through aquatic food web

Microcosms containing DDT spiked-sediment, Tubifex tubifex and carp (Cyprinus carpio) were constructed to simulate a freshwater system. The accumulation, elimination and toxic effects of DDT (p,p'-DDT, o,p'-DDT), and its metabolites DDD (p,p'-DDD, o,p'-DDD) and DDE (p,p'-DDE, o,p'-DDE) were studied in T. tubifex and carp. Tissue/organ distributions of DDTs were also investigated in carp. The bioaccumulation and elimination of DDT differed in T. tubifex, carp and its tissues/organs. Unimodal or bimodal distributions were observed, and the concentrations of DDT metabolites (DDD and p,p'-DDE) increased over time. The carp organ with the highest concentrations of DDTs (DDT, DDD and DDE) was the gill. The largest mass distribution of DDTs was also in gill, followed by muscle and gastrointestinal tract. Maximum levels of DDTs in whole carp and carp muscle were 161 and 87 ng/g, respectively; therefore, the levels of DDTs observed in carp in this study were insufficient to constitute a health concern if present in fish for human consumption. Significant changes were observed in some biomarkers, including superoxide dismutase, catalase, glutathione-S-transferase, glutathione, and carboxylesterase, in T. tubifex and carp tissues during DDT exposure. Tissue-specific accumulation of DDTs in carp can be a key indicator of exposure to environmentally relevant concentrations.

WHO/UNEP global surveys of PCDDs, PCDFs, PCBs and DDTs in human milk and benefit-risk evaluation of breastfeeding

Since 1987, the World Health Organization (WHO) carried out global surveys on polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in human milk. This study presents a review of the three most recent surveys from 2000 to 2010, including DDT. The objective was to identify global quantitative differences and provide baseline information for 52 countries or provide time-trends for countries with previous data. Individual human milk samples were collected following a WHO-designed procedure and combined to form a national pooled sample. Here, we report global levels for PCDDs, PCDFs, PCBs and the sum of o,p'-DDT, p,p'-DDT, o,p'-DDE, p,p'-DDE, o,p'-DDD and p,p'-DDD (ΣDDTs). A concise risk-benefit evaluation related to human milk contamination with these persistent organic pollutants (POPs) was also done. Large global and regional differences were observed. Levels of PCDDs and PCDFs were highest in India and some European and African countries. PCB levels were highest in East and West Europe. The highest levels of ΣDDTs were found in less industrialized countries. A temporal downward trend for PCDDs, PCDFs and PCBs is indicated. A risk-benefit assessment indicates that human milk levels of PCDDs, PCDFs and PCBs are still significantly above those considered toxicologically safe, while ΣDDTs are below or around those considered safe. With respect to potential adverse health effects, a more dominant role of in utero exposure versus lactational exposure is indicated. If potential adverse effects are balanced against positive health aspects for (breastfed) infants, the advantages of breastfeeding far outweigh the possible disadvantages. Our observations provide a strong argument to plea for further global source-directed measures to reduce human exposure further to dioxin-like compounds.