Using in vitro derived enzymatic reaction rates of metabolism to inform pesticide body burdens in amphibians

Estimating dermal contact soil exposure for amphibians

Chemical exposure estimation through the dermal route is an underemphasized area of ecological risk assessment for terrestrial animals. Currently, there are efforts to create exposure models to estimate doses from this pathway for use in ecological risk assessment. One significant limitation has been insufficient published data to characterize exposure and to support the selection and parameterization of appropriate models, particularly for amphibians in terrestrial habitats. Recent publications measuring pesticide doses to terrestrial-phase amphibians have begun to rectify this situation. We collated and summarized available measurements of terrestrial amphibian dermal exposure to pesticides from 11 studies in which researchers measured tissue concentrations associated with known pesticide experimental application rates. This data set included tissue concentrations in 11 amphibian species and 14 different pesticides. We then compared the results of two screening exposure models that differed based on surface area scaling approaches as a function of body weight (one based on birds as surrogates for amphibians and another amphibian-specific) to the measured tissue residue concentrations. We define a false-negative rate for each screening model as the proportion of amphibians for which the predicted concentration is less than the observed concentration (i.e., underestimate), contrary to the intent of screening models, which are intended to have a bias for higher exposure concentrations. The screening model that uses birds as surrogates did not have any instances where estimated expected avian doses were less than measured amphibian body burdens. When using the amphibian-specific exposure model that corrected for differences between avian and amphibian surface area, measured concentrations were greater than model estimates for 11.3% of the 1158 comparisons. The database of measured pesticide concentrations in terrestrial amphibians is provided for use in calculating bioconcentration factors and for future amphibian dermal exposure model development. Integr Environ Assess Manag 2023;19:9-16. © 2022 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Biochemical and cellular responses of the freshwater mussel, Hyriopsis bialata, to the herbicide atrazine

The present study aimed to evaluate biochemical and cellular responses of the freshwater mussel, Hyriopsis bialata, to the herbicide atrazine (ATZ). The mussels were exposed to environmentally-relevant concentrations of ATZ (0, 0.02 and 0.2 mg/L) and a high concentration (2 mg/L) for 0, 7, 14, 21 and 28 days. Tissues comprising male and female gonads, digestive glands and gills were collected and assessed for ethoxyresorufin-O-deethylase (EROD) activity, glutathione S-transferase (GST) activity, multixenobiotic resistance mechanism (MXR), histopathological responses, DNA fragmentation and bioaccumulation of ATZ and its transformation derivatives, desethylatrazine (DEA) and desisopropylatrazine (DIA). Additionally, circulating estradiol levels were determined. It appeared that ATZ did not cause significant changes in activities of EROD, GST and MXR. There were no apparent ATZ-mediated histopathological effects in the tissues, with the exception of the male gonads exhibiting aberrant aggregation of germ cells in the ATZ-treated mussels. Contrarily, ATZ caused significant DNA fragmentation in all tissues of the treated animals in dose- and time-dependent manners. In general, the circulating estradiol levels were higher in the females than in the males. However, ATZ-treated animals did not show significant alterations in the hormonal levels, as compared with those of the untreated animals. Herein, we showed for the first time differentially spatiotemporal distribution patterns of bioaccumulation of ATZ, DEA and DIA, with ATZ and DEA detectable in the gonads of both sexes, DEA and DIA in the digestive glands and only DEA in the gills. The differential distribution patterns of bioaccumulation of ATZ and its derivatives among the tissues point to different pathways and tissue capacity in transforming ATZ into its transformation products. Taken together, the freshwater mussel H. bialata was resistant to ATZ likely due to their effective detoxification. However, using DNA damage as a potential biomarker, H. bialata is a promising candidate for biomonitoring aquatic toxicity.

Route of exposure influences pesticide body burden and the hepatic metabolome in post-metamorphic leopard frogs

Pesticides are being applied at a greater extent than in the past. Once pesticides enter the ecosystem, many environmental factors can influence their residence time. These interactions can result in processes such as translocation, environmental degradation, and metabolic activation facilitating exposure to target and non-target species. Most anurans start off their life cycle in aquatic environments and then transition into terrestrial habitats. Their time in the aquatic environment is generally short; however, many important developmental stages occur during this tenure. Post-metamorphosis, most species spend many years on land but migrate back to the aquatic environment for breeding. Due to the importance of both the aquatic and terrestrial environments to the life stages of amphibians, we investigated how the route of exposure (i.e., uptake from contaminated soils vs. uptake from contaminated surface water) influences pesticide bioavailability and body burden for four pesticides (bifenthrin (BIF), chlorpyrifos (CPF), glyphosate (GLY), and trifloxystrobin (TFS)) as well as the impact on the hepatic metabolome of adult leopard frogs (Gosner stage 46 with 60-90 days post-metamorphosis). Body burden concentrations for amphibians exposed in water were significantly higher (ANOVA p < 0.0001) compared to amphibians exposed to contaminated soil across all pesticides studied. Out of 80 metabolites that were putatively identified, the majority expressed a higher abundance in amphibians that were exposed in pesticide contaminated water compared to soil. Ultimately, this research will help fill regulatory data gaps, aid in the creation of more accurate amphibian dermal uptake models and inform continued ecological risk assessment efforts.

Agrochemical Mixtures and Amphibians: The Combined Effects of Pesticides and Fertilizer on Stress, Acetylcholinesterase Activity, and Bioaccumulation in a Terrestrial Environment

Tank mixtures are popular within the agricultural community because they are time- and cost-effective, but field applications leave nontarget organisms at risk of exposure. We explored the effects of a common herbicide (atrazine and alachlor) and fertilizer (urea) tank mixture on juvenile frog corticosterone stress levels, acetylcholinesterase (AChE) activity, and pesticide bioaccumulation. Single agrochemical or tank mixtures were applied to terrestrial microcosms, and then individual Southern leopard frog (Lithobates sphenocephala) juveniles were added to microcosms for an 8-h exposure. Afterward, frogs were transferred to aquatic microcosms for 1 h to monitor corticosterone prior to euthanasia, brain tissues were excised to evaluate AChE, and tissue homogenates were analyzed for pesticide bioconcentation with gas chromatography-mass spectrometry. Atrazine significantly increased corticosterone in frogs, particularly when combined with alachlor and urea. Atrazine increased AChE and urea decreased AChE, although no interactive effects of chemical combinations were discernible. Relative to their individual treatments, the complete tank mixture with all 3 agrochemicals resulted in 64% greater bioconcentration of atrazine and 54% greater bioconcentration of alachlor in frog tissues. Our results suggest that agrochemical mixtures as well as their active ingredients can lead to altered stress levels and impaired physiological responses in amphibians. An improved understanding of the effects of co-exposure to environmental contaminants in amphibians is important in assessing the ecological risks these compounds pose. Environ Toxicol Chem 2019;9999:1-10. © 2019 SETAC.

Influence of exposure to pesticide mixtures on the metabolomic profile in post-metamorphic green frogs (Lithobates clamitans)

Pesticide use in agricultural areas requires the application of numerous chemicals to control target organisms, leaving non-target organisms at risk. The present study evaluates the hepatic metabolomic profile of one group of non-target organisms, amphibians, after exposure to a single pesticide and pesticide mixtures. Five common-use pesticide active ingredients were used in this study, three herbicides (atrazine, metolachlor and 2,4-d), one insecticide (malathion) and one fungicide (propiconazole). Juvenile green frogs (Lithobates clamitans) were reared for 60-90days post-metamorphosis then exposed to a single pesticide or a combination of pesticides at the labeled application rate on soil. Amphibian livers were excised for metabolomic analysis and pesticides were quantified for whole body homogenates. Based on the current study, metabolomic profiling of livers support both individual and interactive effects where pesticide exposures altered biochemical processes, potentially indicating a different response between active ingredients in pesticide mixtures, among these non-target species. Amphibian metabolomic response is likely dependent on the pesticides present in each mixture and their ability to perturb biochemical networks, thereby confounding efforts with risk assessment.