Phototoxicity identification by solid phase extraction and photoinduced toxicity to Daphnia magna

The response of meiobenthinc sediment-dwelling nematodes to pyrene: Results from open microcosms, toxicokinetics and in silico molecular interactions

An experiment conducted with 'open microcosm' made by connected sedimentary compartments with different qualities was for 30 days to evaluate the migratory behaviour of nematodes as induced by exposure to pyrene. The nematofauna was collected along with sediment from a reference site in Bizerte lagoon. Following one week acclimatization period, the populated sediments were topped with azoic sediments, with a pyrene concentration of 150 μg kg^-1. The concentration of pyrene from sediments was measured on a weekly basis. A stable status of nematode assemblages was reached between the upper and lower compartments in each microcosm, whatever the treatment type. An upward exploratory phase was observed during the first two weeks within the assemblages, possibly induced by the repellent chemodetection of pyrene. This observation was confirmed by the toxicokinetic properties and molecular interactions of pyrene with the germ-line development Protein 3 and sex-determining protein of Caenorhabditis elegans as nematode model.

Monitoring of carbaryl and cypermethrin concentrations in water and soil in Southern Malawi

Carbaryl (a carbamate insecticide) and cypermethrin (a synthetic pyrethroid insecticide) are extensively used in agriculture. However, the presence of these insecticides in the environment constitutes a significant source of ecological contamination. This study determined the levels of these insecticides in Lisungwi, Neno District, a cotton-growing area in Southern Malawi. A total of 81 soil samples (500 g each) were collected from six sampling points (33 in dry season and 48 rainy season). A total of 86 water samples (500 ml each) were collected seasonally (20 from shallow wells, 18 from streams, and 48 from boreholes). High-performance liquid chromatography (HPLC) was used to determine carbaryl while UV/Vis spectrophotometer detected cypermethrin. Paired t test showed a significant (p < 0.05) difference between rainy season carbaryl (in water and soil) and maximum recommended levels (MRL) (Canadian guidelines and Australian Guidelines). Similarly, a significant (p < 0.05) difference between carbaryl and WHO limits and US MRL was reported in water and soil during the rainy season. A similar observation was made for cypermethrin. Specifically, carbaryl (0.083-0.254 mg/L in surface water and 0.165-0.492 mg/L in groundwater) and cypermethrin (8.115-15.460 mg/L in surface water and 4.48-12.18 mg/L in groundwater) concentrations during the rainy season were above the recommended limits. On the other hand, cypermethrin (0.01-0.048 mg/L) in the soil samples during the rainy season was below the recommended limits while carbaryl (1.67-1.305 mg/L) was above the recommended limits. Higher carbaryl and cypermethrin values were recorded during the rainy season than the dry season. Nitrate, pH, and EC and the insecticides (carbaryl and cypermethrin) depicted strong correlation and significance (p < 0.05), suggesting that these factors influenced their persistence in both soil and water. The study provides evidence that Lisungwi has cypermethrin and carbaryl concentrations above the recommended limits and their presence varies with seasons-a situation considered to be a serious threat to both aquatic biota and humans.

Predicting phototoxicity of alkylated PAHs, mixtures of PAHs, and water accommodated fractions (WAF) of neat and weathered petroleum with the phototoxic target lipid model

The toxicity of petroleum can increase considerably after exposure to solar radiation, during which certain components in the mixture, including polycyclic aromatic hydrocarbons (PAHs), absorb light in ultraviolet and visible portions of the solar radiation spectrum. A phototoxic target lipid model (PTLM), previously developed to predict the phototoxicity of single PAHs, is validated for 4 species (Americamysis bahia, Rhepoxynius abronius, Daphnia magna, and Pimephales promelas) exposed to 12 compounds that are components of petroleum, including alkylated PAHs and dibenzothiophene. The PTLM is also used to predict the phototoxicity of binary and ternary mixtures of 3 PAHs, pyrene, anthracene, and fluoranthene, to A. bahia and Menidia beryllina. Finally, it is used to predict the toxicity of water accommodated fractions of neat and naturally weathered Macondo crude oil samples from the Deepwater Horizon oil spill sites. The Gulf of Mexico species, including A. bahia, M. beryllina, Cyprinodon variegatus, and Fundulus grandis were exposed to the oil samples under natural and simulated solar radiation. The results support the applicability of the PTLM for predicting the phototoxicity of petroleum. Environ Toxicol Chem 2018;37:2165-2174. © 2018 SETAC.

A critical review of polycyclic aromatic hydrocarbon phototoxicity models

Polycyclic aromatic hydrocarbons (PAHs) are known to exhibit photo-induced toxicity. Hundreds to thousands of PAH parent and substituted compounds are found in the environment, and developing a predictive model applicable to a wide variety of PAHs and organisms is a necessary precursor to environmental risk assessments. There has been evolutionary progress in phototoxicity modeling since 1977. In the present study, a comprehensive review of the models developed to predict phototoxicity of PAHs is presented. The contributions of each of the models to the state of the art are discussed. The models are compared in terms of their scope of applicability to different organisms, PAHs, endpoints (median lethal time and median lethal concentration), and light conditions. The current state of the science that accounts for the key elements of phototoxicity modeling, including the differences in species sensitivity, the partitioning of PAHs into the target lipid of the organisms, and light absorption by the chemicals, as well as light exposure time and conditions, is discussed. In addition, the remaining issues that need to be addressed are explored: the effect of time-varying exposures to light and PAH concentrations, and the lack of a mechanistic understanding that can explain the failure of the Bunsen-Roscoe law of reciprocity. Environ Toxicol Chem 2017;36:1138-1148. © 2016 SETAC.

Phototoxic target lipid model of single polycyclic aromatic hydrocarbons

A phototoxic target lipid model (PTLM) is developed to predict phototoxicity of individual polycyclic aromatic hydrocarbons (PAHs) measured either as median lethal concentration (LC50) or median lethal time (LT50) for a 50% toxic response. The model is able to account for the differences in the physical/chemical properties of PAHs, test species sensitivities, and variations in light source characteristics, intensity, and length of exposure. The PTLM is based on the narcotic target lipid model (NTLM) of PAHs. Both models rely on the assumption that mortality occurs when the toxicant concentration in the target lipid of the organism reaches a threshold concentration. The PTLM is applied to observed LC50s and LT50s for 20 individual PAHs, 15 test species-including arthropods, fishes, amphibians, annelids, mollusks, and algae-exposed to simulated solar and various UV light sources, for exposure times varying from less than 1 h to 100 h, a total of 333 observations. The LC50 concentrations range from less than 0.1 µg/L to greater that 10⁴  µg/L. The model has 2 fitting parameters that are constant and apply to all PAHs and organisms. The root mean square errors of prediction for log(LC50) and log(LT50) are 0.473 and 0.382, respectively. The results indicate that the PTLM can predict the phototoxicity of single PAHs over a wide range of exposure conditions and to organisms with a wide range of sensitivities. Environ Toxicol Chem 2017;36:926-937. © 2016 SETAC.

Comparison of species sensitivity distributions constructed with predicted acute toxicity data from interspecies correlation estimation models and measured acute data for benzo[a]pyrene

Benzo[a]pyrene (BaP) is a priority Polycyclic Aromatic Hydrocarbon (PAH), which is toxic to aquatic organisms and has been widely detected in the environment. However, ecological risk assessment for BaP is hard to perform because of the absence of water quality criteria (WQC) and lack of toxicity data for this chemical. To fill in the data gaps, a interspecies correlation estimation (ICE) model was developed by USEPA to predict toxicity values for multiple species from the toxicity estimate for one species. In order to validate the applicability of the ICE model for BaP, measured-based-species sensitivity distributions (SSDs) generated using eight Chinese native aquatic species were compared with ICE-based-SSDs generated using the data predicted from three surrogate species (Lepomis macrochirus, Cyprinus carpio and Daphnia magna). The results showed that there were no significant differences between the two SSD curves and the two hazardous concentrations for the 5% of species (HC5) derived from measured acute toxicity data and ICE-based predicted data. The ICE model was verified as a valid approach for generating SSDs with limited toxicity data.

Fate and effects of 2,4,6-trinitrotoluene (TNT) from dumped ammunition in a field study with fish and invertebrates

2,4,6-Trinitrotoluene (TNT) is the major explosive ingredient in ammunition dumped into lakes and sea after World War II. The aim of the present field study was to study the fate and effect of TNT and its degradation products from dumped ammunition. Artillery shells were cleaved longitudinally to expose TNT and placed in open boxes filled with sediment, and then placed at the sea bottom. Sediment samples were taken in each box at the start and after 3, 9, 13, 20, 24, 33, and 36 months, and the sediments were tested for toxicity with bioassays using Nitocra spinipes (96 h), Hyalella azteca (96 h), and Daphnia magna (24 and 48 h). The result from the bioassays showed no impact of dumped ammunition on the survival of H. azteca and mobility of D. magna. Bioassays with N. spinipes showed significant differences in toxicity between control boxes and boxes with shells after 9 months and thereafter. The mean mortality (+/- SD) of N. spinipes in boxes with shells was 63 +/- 22%, and the mortality in control boxes was 23 +/- 17%. No continuous increase in sediment toxicity over time was found. After 3 years, cages with European flounder (Platichtys flesus) and blue mussels (Mytilus edulis) were attached to the boxes. The fish were examined for biochemical and physiological effects 8 weeks later. Exposure to ammunition, which had rested on the sea bottom 3 years, caused no significant effects on body indices, hematological variables, and detoxification and antioxidant enzymes activities in the flounder. The sediment, bile, and blood plasma of exposed fish, and hepatopancreas of exposed mussels, contained no detectable levels of TNT and its metabolites. Only minor disappearance of TNT from the shells could be detected by visual inspection on site (by scuba divers). This study suggests that the survival of sensitive benthic organisms, e.g., N. spinipes, might be negatively affected at an ammunition dumping site.

Tentative biomarkers for 2,4,6-trinitrotoluene (TNT) in fish (Oncorhynchus mykiss)

2,4,6-Trinitrotoluene (TNT) is the major explosive in ammunition dumped into lakes and the sea after World War II. To identify useful biomarkers of TNT-exposure for forthcoming fish monitoring studies at ammunition dumping sites, rainbow trout (Oncorhynchus mykiss) were intraperitoneal (i.p.) injected with TNT in peanut oil at doses of 0, 100, 200 or 400 mg TNT/kg body weight and sampled 72 h later. The study covered blood parameters, and hepatic antioxidant and detoxifying enzymes. Fish treated with TNT had an increased glutathione S-transferase (GST) activity and glutathione reductase (GR) activity, and a decreased percentage of oxidised glutathione (%GSSG) compared to the control group. In addition to increased methemoglobin, the increased glutathione and glutathione dependent enzyme activities indicate that TNT oxidises macromolecules and activates antioxidant defence systems which may be useful as general biomarkers of TNT-exposure. The fish bile was analysed for TNT and its metabolites by gas chromatography-mass spectrometry (GC-MS), and the toxicity of the bile was determined with the cladoceran Ceriodaphnia dubia. A dose-dependent increase in TNT, 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT) was found in the hydrolysed bile of the TNT-treated fish. These results indicate that the fish are able to detoxify and excrete TNT and suggest that the detection of TNT, 2-ADNT and 4-ADNT in bile may be suitable as a direct marker of exposure to TNT.

Quantitative structure-property relationships on photolysis of PCDD/Fs adsorbed to spruce (Picea abies (L.) Karst.) needle surfaces under sunlight irradiation

By partial least squares (PLS) regression, quantitative structure-property relationship (QSPR) models were developed for photolysis half-life (t1/2) of PCDD/Fs and PAHs sorbed to spruce (Picea abies (L.) Karst.) needle surfaces and irradiated by sunlight. Quantum chemical descriptors computed by PM3 Hamiltonian were used predictor variables. PLS analysis for the PCDDs and PAHs respectively resulted in no correlation by our statistical methods. The cross-validated Qcum2 value for the optimal QSPR model of PCDFs is 0.722, indicating a good predictive ability for logt1/2 of PCDFs adsorbed to spruce needle surfaces. The QSPR results show that the number of chlorine atoms bonded to the parent structure and (E(LUMO)-E(HOMO))2 has a dominant effect on t1/2 values of PCDFs. Increasing the number of chlorine atoms and (E(LUMO)-E(HOMO))2 values leads to increase of logt1/2 values of PCDFs.

Environmental labeling of car tires--toxicity to Daphnia magna can be used as a screening method

Car tires contain several water-soluble compounds that can leach into water and have toxic effects on aquatic organisms. Due to tire wear, 10,000 tonnes of rubber particles end up along the Swedish roads every year. This leads to a diffuse input of emissions of several compounds. Emissions of polyaromatic hydrocarbons (PAHs) are of particular concern. PAHs are ingredients of the high aromatic oil (HA oil) that is used in the rubber as a softener and as a filler. The exclusion of HA oils from car tires has started, and an environmental labeling of tires could make HA oils obsolete. The toxicity to Daphnia magna from 12 randomly selected car tires was tested in this study. Rubber from the tread of the tires was grated into small pieces, to simulate material from tire wear, and the rubber was equilibrated with dilution water for 72 h before addition of test organisms. The 24-h EC50s of the rubber pieces ranged from 0.29 to 32 gl-1, and the 48-h EC50s ranged from 0.0625 to 2.41 gl-1. Summer tires were more toxic than winter tires. After the 48-h exposure, the daphnids were exposed to UV-light for 2 h, to determine if the tires contained compounds that were phototoxic. After UV-activation the EC50s ranged from 0.0625 to 0.38 gl-1. Four of the 12 tires had a very distinct photoactivation, with a toxicity increase of >10 times. This study has shown that the used method for toxicity testing with Daphnia magna according to ISO 6341 could be used as a basis for environmental labeling of car tires.

High sensitivity of northern pike larvae to UV-B but no UV-photoinduced toxicity of retene

In order to investigate whether increased UV-B radiation is a risk factor, a series of acute laboratory experiments was conducted with larval stages of the northern pike (Esox lucius L.), hatching in Nordic waters in May. Further, a comparative investigation on the acute phototoxicity of retene (7-isopropyl-1-methylphenanthrene), a PAH compound recently revealed to posses UV-B-induced phototoxicity in larval coregonids, was conducted with pike larvae. In semi-static experiment, larvae were pre-exposed to retene (3, 9, 30 and 82 microg/g), with relevant controls, for 24 h and then irradiated for 3 h once a day (two consecutive days) with three UV-B doses (CIE-weighted 1.0, 1.8 or 2.7 kJ/m2 per day) or with visible light only. In 3 days, the UV-B exposure alone increased mortality by 10-20% in all applied dose rates. Retene (up to 82 microg/l) had no direct UV-B-induced toxicity in pike. However, pike larvae were very sensitive to UV-B even in low doses, indicated as severe neurobehavioral disorders. Monitoring of pike with the neurobehavioral syndrome revealed substantial late mortality. As UV-B had no influence on CYP1A content in larval pike, retene (9-82 microg/l) induced this protein substantially with and without UV-B. In pike, the applied UV-B radiation and water retene alone both decreased HSP70 concentrations. Neither UV nor retene changed SOD activity significantly. Overall, data on pike suggest that only a minor increase in ambient UV-B coming to the earth's surface may cause lethal effects to larval fish.

Photolysis of polycyclic aromatic hydrocarbons adsorbed on spruce [Picea abies (L) Karst] needles under sunlight irradiation

Photolysis of polycyclic aromatic hydrocarbons (PAHs) sorbed on surfaces of spruce [Picea abies (L.) Karst.] needles under sunlight irradiation was investigated. PAHs were produced by combustion of polyvinyl chloride (PVC), wood, high-density polyethylene (HDPE), and styrene in a stove. The factors of sunlight irradiation on the surfaces of spruce needles were taken into consideration when investigating the kinetic parameters. The photolysis of the 18 PAHs under study follows first-order kinetics. The photolysis half-lives range from 15 h for dibenzo(a,h)anthracene to 75 h for phenanthrene. Photolysis of some PAHs on surfaces of spruce needles may play an important role on the fate of PAHs in the environment.

PAH phototoxicity--an ecologically irrelevant phenomenon?

Photoenhanced toxicity of polycyclic aromatic hydrocarbons (PAH) is well demonstrated in laboratory and in a few in situ studies. Effects have been observed for multiple taxa and toxicological endpoints, and the mechanism of toxic action has been described. However, this phenomenon is ameliorated by physical, chemical and biotic factors. The ecological relevance of PAH phototoxicity remains uncertain; it should not be used for environmental management decisions unless its ecological relevance is firmly established, and then only as part of a weight of evidence determination.

Additive toxicity of binary mixtures of phototoxic polycyclic aromatic hydrocarbons to the oligochaete Lumbriculus variegatus

Toxicity of some polycyclic aromatic hydrocarbons (PAHs) can increase by an order of magnitude, or more, in the presence of solar ultraviolet (UV) radiation. In the environment, PAHs exist as complex mixtures, which generally would include multiple PAHs that could cause photoinduced toxicity. Hence, to accurately predict the potential ecological risk of phototoxic PAHs, it is critical to understand their joint toxicity. In this study, we exposed the oligochaete Lumbriculus variegatus to the phototoxic PAHs anthracene, fluoranthene, and pyrene, both singly and as binary mixtures for 96 h. Following this, the animals were exposed to UV light for an additional 96 h, during which periodic observations of mortality were made. Time-dependent phototoxicity of the binary PAH mixtures, expressed as a function of the product of UV light intensity and PAH dose (in the tissue of the animals), was adequately described using a concentration addition model. Given the probability that the PAHs examined acted via a common mechanism of action, this result was consistent with expectations. These data highlight the need to consider the combined photoactivation potential of PAH mixtures and provide the technical basis for a modeling approach to predict their ecological risk.

Effects of different protective agents on the phototoxicity of fluoranthene to Daphnia magna

Some compounds, accumulated by organisms, are transformed into toxic forms when irradiated with UV light. The polycyclic aromatic hydrocarbon (PAH) fluoranthene is one such compound of environmental importance. In this study on Daphnia magna, fluoranthene toxicity increased significantly after a 2 h exposure to solar-simulating UV light, if organisms were allowed to accumulate the substance for 24 h prior to irradiation. Since no enhanced toxicity was observed if the solutions were irradiated before the daphnids were added and only a slight decrease in toxicity was observed if the daphnids were transferred to pure dilution water prior to exposure, it was concluded that the acute phototoxicity of fluoranthene was predominantly due to photoactivation of accumulated or adsorbed molecules. Thus, the enhanced toxicity of fluoranthene by UV light is thought to act through the production of either singlet oxygen or free radicals. Possible effects of different protective agents (antioxidants, free radical scavengers and UV-screening compounds) were examined in two cultured populations of Daphnia magna. One population received a synthetic diet and the other dried baker's yeast. The yeast-fed population became progressively more sensitive to the photoinduced toxicity of fluoranthene, and after 14 days it was significantly more sensitive than the population that received the synthetic feed. It was not obvious whether any of the additives influenced the UV-induced toxicity significantly, although, alpha-tocopherol, a known antioxidant, was the best candidate.