Linking organochlorine exposure to biomarker response patterns in Anurans: a case study of Müller's clawed frog (Xenopus muelleri) from a tropical malaria vector control region

Chemical contaminants and environmental stressors induced teratogenic effect in aquatic ecosystem - A comprehensive review

Aquatic environments, including marine and freshwater ecosystems, are vital for ecological balance and biodiversity. The rising global demand for aquaculture products necessitates increased production, with intensified aquaculture practices posing significant environmental risks. This review explores the pathways through which chemical pollutants, heavy metals, pharmaceuticals, and environmental stressors induce teratogenic effects in aquatic species. The review highlights the impact of pesticide include triazine herbicides, organophosphate and organochlorine insecticides, and carbamates on aquatic life, emphasizing their interference with endocrine systems and developmental processes. Heavy metals like mercury, lead, cadmium, arsenic, and chromium are noted for their persistence and bioaccumulative properties, disrupting cellular and hormonal functions. Pharmaceuticals, including NSAIDs, antibiotics, and chemotherapeutic agents, exert teratogenic effects by disrupting physiological and developmental pathways. Environmental stressors includes temperature fluctuations, salinity variations, pH changes, and oxygen level imbalances exacerbate the teratogenic impact of pollutants. This review highlights the importance of comprehensive environmental management and understanding these complex interactions is essential for formulating efficient strategies to safeguard the effective measures to protect aquatic ecosystems and the biodiversity.

The benefit of using in vitro bioassays to screen agricultural samples for oxidative stress: South Africa's case

Applied pesticides end up in non-target environments as complex mixtures. When bioavailable, these chemicals pose a threat to living organisms and can induce oxidative stress (OS). In this article, attention is paid to OS and the physiological role of the antioxidant defense system. South African and international literature was reviewed to provide extensive evidence of pesticide-induced OS in non-target organisms, in vivo and in vitro. Although in vitro approaches are used internationally, South African studies have only used in vivo methods. Considering ethical implications, the authors support the use of in vitro bioassays to screen environmental matrices for their OS potential. Since OS responses are initiated and measurable at lower cellular concentrations compared to other toxicity endpoints, in vitro OS bioassays could be used as an early warning sign for the presence of chemical mixtures in non-target environments. Areas of concern in the country could be identified and prioritized without using animal models. The authors conclude that it will be worthwhile for South Africa to include in vitro OS bioassays as part of a battery of tests to screen environmental matrices for biological effects. This will facilitate the development and implementation of biomonitoring programs to safeguard the South African environment.

Development and application of a mini-QuEChERS method for the determination of pesticide residues in anuran adipose tissues

The expansion of monocultures to regions close to conservation areas has put biodiversity at risk, mainly due to the intense use of pesticides. Anurans are highly susceptible to pesticides and may be a biological marker in the contamination of an area. However, methods for determining pesticides in anurans are incipient. In this work, a miniaturized QuEChERS method was developed for the extraction of atrazine, chlorpyrifos, α- and β-endosulfan, α-, β-, θ- and ζ-cypermethrin in anuran adipose tissues. The method was optimized for the tissue sample size scale according to sample mass availability. Extracting solvent and adsorbents for the clean-up step was evaluated, achieving recoveries next to 100% with acetonitrile and without a clean-up step. The mini-QuEChERS method, using 500 mg of adipose tissue, 50 mg of NaCl and 200 mg of MgSO4, 100 μL of ultrapure water, and 1.50 mL of acetonitrile with no purification step, followed by high-performance liquid chromatography analysis and photodiode array detection was validated following the European Community guidelines. The methodology showed a moderate matrix effect for some pesticides, which was corrected using the matrix-matched calibration. The limits of quantification for the pesticide residues in adipose tissues ranged from 10 to 75 μg kg-1. Pesticide recoveries ranged from 74% to 115%, and repeatability and within-lab reproducibility showed relative standard deviations < 11%. The mini-QuEChERS method was applied to extract pesticide residues from the adipose tissues of two species of anurans: Leptodactylus macrosternum and Scinax x-signatus. 25% of samples were positive, detecting endosulfan and chlorpyriphos, confirmed by liquid chromatography coupled to tandem mass spectrometry. The mini-QuEChERS was a simple, economical, and eco-friendly method for extracting pesticide residues in anuran adipose tissue samples.

Immuno-endocrine alterations and oxidative stress induced by commercial formulations of pesticides in the tegu lizard (Salvator merianae)

Recent research has shown the risk of environmental contamination by pesticides in Argentina. Salvator merianae is considered as "sentinel species" for monitoring their effects. We intended to investigate growth, immunological and endocrine functions, and oxidative stress in S. merianae exposed to two commercial brands of the herbicide glyphosate: Roundup and Panzer Gold, as well as, to two insecticides: chlorpyrifos, and cypermethrin. Our results showed a higher increase in growth in animals exposed to Roundup and chlorpyrifos and a lower increase in those exposed to Panzer Gold. Higher total leukocyte and lymphocyte count values were observed in lizards exposed to Panzer Gold. The heterophils/lymphocytes ratio decreased in all treated animals. Regarding lobularity index, natural antibodies titers, and complement system activity values, lizards exposed to cypermethrin had higher values. Low corticosterone levels were observed in animals exposed to Roundup. Our results reveal different toxic effects of pesticides contributing to the knowledge of the pesticides' potential deleterious impact in the habitat of S. merianae.

Levels of persistent organic pollutants in cane toads (Rhinella marina) differ among sites with varying industrial and agricultural activities

In this study, we captured cane toads (Rhinella marina) in four sites located in different regions affected by anthropogenic activities in Mexico. Subsequently we analyzed liver tissue for the presence of organochlorine pesticides (OCs) and polychlorinated biphenyls (PCBs) The levels of these POPs in the toads' livers ranged from 863.2 to 3109.6 ng/g of lipid weight across all sites. A multivariate statistical analysis highlighted two sites with the highest POPs levels, with the most polluted site displaying a high level of PCBs, suggesting influence of industrial activities. The second most polluted site displayed significant amounts of OCs, linking this location to agricultural activity. Additionally, we found pesticide metabolites and isomers that allowed us to distinguish past and recent exposure events. Our observations indicate that R. marina is suitable bioindicator of sites impacted by anthropogenic activities.

Emerging concepts and opportunities for endocrine disruptor screening of the non-EATS modalities

Endocrine disrupting chemicals (EDCs) are ubiquitous in the environment and involve diverse chemical-receptor interactions that can perturb hormone signaling. The Organization for Economic Co-operation and Development has validated several EDC-receptor bioassays to detect endocrine active chemicals and has established guidelines for regulatory testing of EDCs. Focus on testing over the past decade has been initially directed to EATS modalities (estrogen, androgen, thyroid, and steroidogenesis) and validated tests for chemicals that exert effects through non-EATS modalities are less established. Due to recognition that EDCs are vast in their mechanisms of action, novel bioassays are needed to capture the full scope of activity. Here, we highlight the need for validated assays that detect non-EATS modalities and discuss major international efforts underway to develop such tools for regulatory purposes, focusing on non-EATS modalities of high concern (i.e., retinoic acid, aryl hydrocarbon receptor, peroxisome proliferator-activated receptor, and glucocorticoid signaling). Two case studies are presented with strong evidence amongst animals and human studies for non-EATS disruption and associations with wildlife and human disease. This includes metabolic syndrome and insulin signaling (case study 1) and chemicals that impact the cardiovascular system (case study 2). This is relevant as obesity and cardiovascular disease represent two of the most significant health-related crises of our time. Lastly, emerging topics related to EDCs are discussed, including recognition of crosstalk between the EATS and non-EATS axis, complex mixtures containing a variety of EDCs, adverse outcome pathways for chemicals acting through non-EATS mechanisms, and novel models for testing chemicals. Recommendations and considerations for evaluating non-EATS modalities are proposed. Moving forward, improved understanding of the non-EATS modalities will lead to integrated testing strategies that can be used in regulatory bodies to protect environmental, animal, and human health from harmful environmental chemicals.

Sub-lethal exposure to malaria vector control pesticides causes alterations in liver metabolomics and behaviour of the African clawed frog (Xenopus laevis)

In this study we explore the sub-lethal effects of two malaria vector control pesticides, deltamethrin and dichlorodiphenyltrichloroethane (DDT), on Xenopus laevis by incorporating different levels of biological organisation. Pesticide accumulation in frog tissue was measured alongside liver metabolomics and individual swimming behaviour to assess whether changes presented at these different levels, and if such changes could be linked between levels. Results showed evidence of concentration dependent accumulation of DDT and its metabolites, but no measurable accumulation of deltamethrin in adult X. laevis after 96 h of exposure. Both DDT and deltamethrin were shown to cause alterations in the liver metabolome of X. laevis. We also showed that some of these changes can be enhanced in exposure to a mixture of these two pesticides. Initial behavioural responses recorded directly after exposure were seen in the form of decreased activity, less alterations between mobility states, and less time spent at the water surface. This response persisted after 96 h of exposure to a mixture of the two pesticides. This study shows that sub-lethal exposure to pesticides can alter the biochemical homeostasis of frogs with the potential to cascade onto behavioural and ecological levels in mixture exposure scenarios.

Regional Scale Risk to the Ecological Sustainability and Ecosystem Services of an African Floodplain System

The Phongolo floodplain is one of southern Africa's most important systems. In this study, we carried out a regional scale ecological risk assessment to evaluate the risk of multiple stressors associated with the use of the aquatic resources in the floodplain to selected social and ecological endpoints representing its sustainability. The floodplain has undergone significant changes as a result of the impacts of multiple stressors. This includes high risk of impact and threatened sustainability between the Pongolapoort Dam and the Ndumo Game Reserve (NGR). This compares to relatively low risk to the maintenance of the endpoints within the NGR. The reserve provides a protection and refuge function for regional biodiversity maintenance and ecosystem sustainability processes. In the study a range of scenarios were considered and demonstrate that the system will respond to protection measures and or increased resource use options. Should flood reductions or water quality pollution drivers continue on increasing trajectories, the condition of the Phongolo River and floodplain will probably deteriorate into an unacceptable, unsustainable state. Removal of the protection services of the NGR would result in an unsustainable ecosystem and loss of ecosystem services for regional vulnerable African communities. Additional evidence should be obtained from monitoring and research to refine, validate, and update the assessment in an adaptive management context. The risk assessment framework approach implemented in the Phongolo floodplain can contribute to the management of other floodplains ecosystems and the sustainability management of social and ecological attributes and processes of these important ecosystems.

Bioaccumulation of DDT and other organochlorine pesticides in amphibians from two conservation areas within malaria risk regions of South Africa

The threat to wildlife from chemical exposure exists regardless of the presence of conservation boundaries. An issue exacerbated by the use of environmentally persistent insecticides for vector control and long-range transport of legacy persistent organic pollutants. In this comparative study between two important conservation regions in South Africa, Kruger National Park (KNP) and Ndumo Game Reserve (NGR), we assessed organochlorine pesticide (OCP) accumulation in several anuran species collected from within the conservation regions. The two conservation regions differ in size and subsequent proximity of collection sites to OCP input sources. Detectable concentrations of OCPs were present in ∼ half the frogs analysed from KNP and ∼all frogs from NGR and total OCP loads were similar between regions, where measured in the same species. The OCP profiles in KNP frogs were representative of legacy pesticides likely introduced via long-range transport, whereas NGR profiles showed influence of current use of DDT consistent with close proximity to sources. This indicates amphibians can accumulate OCPs within conservation regions and that the exposure of non-target organisms inside conservation regions to current use pesticides has a strong association with proximity to sources. These results serve to inform conservation management decision making with regard to the non-target organism effects of chemical interventions such as vector control pesticide use in and around conservation regions.

Agrochemicals disrupt multiple endocrine axes in amphibians

Concern over global amphibian declines and possible links to agrochemical use has led to research on the endocrine disrupting actions of agrochemicals, such as fertilizers, fungicides, insecticides, acaricides, herbicides, metals, and mixtures. Amphibians, like other species, have to partition resources for body maintenance, growth, and reproduction. Recent studies suggest that metabolic impairments induced by endocrine disrupting chemicals, and more particularly agrichemicals, may disrupt physiological constraints associated with these limited resources and could cause deleterious effects on growth and reproduction. Metabolic disruption has hardly been considered for amphibian species following agrichemical exposure. As for metamorphosis, the key thyroid hormone-dependent developmental phase for amphibians, it can either be advanced or delayed by agrichemicals with consequences for juvenile and adult health and survival. While numerous agrichemicals affect anuran sexual development, including sex reversal and intersex in several species, little is known about the mechanisms involved in dysregulation of the sex differentiation processes. Adult anurans display stereotypical male mating calls and female phonotaxis responses leading to successful amplexus and spawning. These are hormone-dependent behaviours at the foundation of reproductive success. Therefore, male vocalizations are highly ecologically-relevant and may be a non-invasive low-cost method for the assessment of endocrine disruption at the population level. While it is clear that agrochemicals disrupt multiple endocrine systems in frogs, very little has been uncovered regarding the molecular and cellular mechanisms at the basis of these actions. This is surprising, given the importance of the frog models to our deep understanding of developmental biology and thyroid hormone action to understand human health. Several agrochemicals were found to have multiple endocrine effects at once (e.g., targeting both the thyroid and gonadal axes); therefore, the assessment of agrochemicals that alter cross-talk between hormonal systems must be further addressed. Given the diversity of life-history traits in Anura, Caudata, and the Gymnophiona, it is essential that studies on endocrine disruption expand to include the lesser known taxa. Research under ecologically-relevant conditions will also be paramount. Closer collaboration between molecular and cellular endocrinologists and ecotoxicologists and ecologists is thus recommended.

Serum level of PCBs and OCPs and leukocyte telomere length among adults in Tehran, Iran

Exposure to polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) may change leukocyte telomere length (TL) at the end of the DNA sequence. The purpose of this study was to investigate the association between PCBs and OCPs exposure with TL in Tehran adult males. Whole-blood samples were randomly taken from three hundred adult males in population-based cross-section study from October 2016 to November 2017. We studied the serum levels of PCBs, OCPs as well as socio-demographic characteristics of individuals. The quantitative PCR was used to investigate the number of the telomere (T) repeats to the number of a single copy gene. We measured the effect of each PCBs and OCPs congeners on TL using linear regressions adjusted for age, BMI, smoking, and dietary patterns. The median level of the six non-dioxin-likes, five dioxin-likes PCBs three OCPs and TL in the study population were 344.5, 306.0, 45.0 ng/g lipid and 5377.7 ± 573.4 base pairs, respectively. In the adjusted model, the percent difference in the TLs with exposure to Σnon-dioxin-like PCBs, Σdioxin-like PCBs, and OCPs were 1.93 (-0.70 to 5.4), 3.4 (1.8-8.3) and -2.4 (-0.80 to -6.2), respectively. In the fourth quartile compared to the first quartile, the percent difference in the TLs due to Σnon-dioxin-like PCBs, Σdioxin-like PCBs, and OCP exposure were 0.01 (-0.01 to 0.05), 10.3 (2.9-18.1) and -0.20 (-0.10 to -4.5), respectively. Exposures to ndl-PCBs and dl-PCBs (except for PCB28) were related to longer TLs, but OCPs exposure can be related to telomere shortening.

Biomarker Responses in the Freshwater Shrimp Caridina nilotica as Indicators of Persistent Pollutant Exposure

Biomarkers are applied as early warning indicators of organisms' exposure to pollutants. The aim of this study was to utilise a multi-biomarker approach in the freshwater shrimp Caridina nilotica (Decapoda: Atyidae) as indicators of persistent pollutant exposure. A suite of biomarkers was selected to cover oxidative stress and damage, and energetics of the organisms. Five sites, representing an agricultural and pesticide application gradient, were sampled during two flow related hydro-periods in rivers of the Phongolo floodplain, north-eastern South Africa. Cytochrome P450 (CYP) activity was significantly higher in shrimp at sites directly adjacent to regions of increased human activity. Increased oxidative responses, i.e. catalase (CAT; p < 0.01) and protein carbonyl (PC, p < 0.01) were also found at these sites. The energetics biomarker did not show any influence of increased contaminant exposure. We demonstrated that the biomarkers of exposure (CYP) and effect (CAT, PC) were suitable to detect effects of stressors, probably persistent pollutants.

Current Status and Future Prognosis of Malaria Vector Control Pesticide Ecotoxicology and Xenopus sp

Anurans from the genus Xenopus have long been used as standard testing organisms and occur naturally in tropical and sub-tropical areas where malaria vector control pesticides are actively used. However, literature on the toxic effects of these pesticides is limited. This review analyses the available data pertaining to both Xenopus and the pesticides used for malaria vector control in order to determine the pesticides that have the greatest potential to influence amphibian health while also identifying gaps in literature that need to be addressed. Amphibian diversity has shown the fastest decline of any group, yet there are still voids in our understanding of how this is happening. The lack of basic toxicity data on amphibians with regard to pesticides is an issue that needs to be addressed in order to improve effectiveness of amphibian conservation strategies. Meta-analyses performed in this review show that, at current usage, with the available acute toxicity literature, the pyrethroid pesticide group could hold the highest potential to cause acute toxicity to Xenopus sp. in relation to the other MVCPs discussed, but the lack of data cripples the efficacy with which meta-analyses can be performed and conclusions made from such analyses. Several studies have shown that DDT accumulates in Xenopus sp. from malaria vector control areas, but accumulation of other MVCPs in frogs is still largely unknown. Through this review we hope to encourage future research into the field of amphibian ecotoxicology and to promote the use of the Xenopus standard model in order to build comprehensive datasets that may be used in amphibian conservation.

Assessing predator-prey interactions in a chemically altered aquatic environment: the effects of DDT on Xenopus laevis and Culex sp. larvae interactions and behaviour

Behavioural assays are used as a tool to understand ecotoxicological effects on organisms, but are often not applied in an ecologically relevant context. Assessment of the effect of chemical contaminants on behaviours relating to fitness and trophic interactions for example, requires incorporating predator-prey interactions to create impact assessments. Dichlorodiphenyltrichloroethane (DDT) is a controlled substance but is still regularly used as a form of mosquito control. There is little explicit information on the effect of DDT on animal behaviour and the consequent effects upon trophic interactions. This study uses a 3 × 2 factorial design to assess the feeding behaviour of Xenopus laevis toward Culex sp. larvae when supplied with different prey cues. We also assess the behavioural responses of mosquito larvae when supplied with no threat cue and predator threat cues when exposed to 0 µg/L, 2 µg/L and 20 µg/L DDT. There was a significant "DDT exposure" x "prey cue" interaction whereby DDT significantly decreased the foraging behaviour of X. laevis towards live prey cues, however there was no effect of DDT on X. laevis response to olfactory prey cues. Dichlorodiphenyltrichloroethane exposure caused mosquito larvae to appear hyperactive regardless of DDT concentration. Mosquito larvae anti-predator response was significantly dampened when exposed to 2 µg/L DDT, however when exposed to 20 µg/L the anti-predator responses were not impaired. Our results indicate a complex interplay in trophic interactions under DDT exposure, wherein effects are mediated depending on species and concentration. There are possible implications regarding reduced anti-predator behaviour in the prey species but also reduced foraging capacity in the predator, which could drive changes in ecosystem energy pathways. We demonstrate that in order to quantify effects of pesticides upon trophic interactions it is necessary to consider ecologically relevant behaviours of both predator and prey species.

Evidence of impacts from DDT in pelican, cormorant, stork, and egret eggs from KwaZulu-Natal, South Africa

DDT remains in use for malaria control in South Africa. We quantified DDTs in aquatic bird eggs from the highly biodiverse northern KwaZulu-Natal, a province of South Africa where DDT has been used for more than 80 years for malaria control. Pelican eggs had the highest ΣDDT concentration (7200 ng/g lipid mass; lm), Little Egret eggs had 6900 ΣDDT lm, African Openbill eggs had 3400 ng/g lm ΣDDT, and White-breasted Cormorant had 2400 ng/g lm. All species had non-significantly different mean concentrations of o,p'-DDT, p,p'-DDT, and ΣDDT, but with significant differences for p,p-DDE, o,p'-DDD, p,p'-DDD, %DDT, %DDD, and %lipid. The thinnest pelican eggshell (0.40 mm) had a ΣDDT concentration of 3300 ng/g lm.; the thickest shell (0.96 mm) had the lowest ΣDDT concentration at 29 ng/g lm; a 58% difference. Linear regressions of concentrations with shell thickness for the pelican eggs were significant for p,p'-DDE and p,p'-DDD, indicating risk of reproductive impairment. Compositional profiles indicate different food webs for the different species. DDT concentrations were lower than from another DDT-sprayed locality in South Africa, possible linked to differences in hydrology and rainfall. We conclude that significant ecotoxic threats associated with DDT remain in this area, and possibly threatens birds from less polluted areas. Our findings suggest continued negative human health and environmental impacts from DDT. There is an urgency to move away from DDT as quickly as possible; alternatively, to implement practices that prevent emissions of DDT to the environment while protecting human life.