Predicting herbicide mixture effects on multiple algal species using mixture toxicity models

Environmental health and risk assessment metrics with special mention to biotransfer, bioaccumulation and biomagnification of environmental pollutants

The environment pollutants, which are landed up in environment because of human activities like urbanization, mining and industrializations, affects human health, plants and animals. The living organisms present in environment are constantly affected by the toxic pollutants through direct contact or bioaccumulation of chemicals from the environment. The toxic and hazardous pollutants are easily transferred to different environmental matrices like land, air and water bodies such as surface and ground waters. This comprehensive review deeply discusses the routes and causes of different environmental pollutants along with their toxicity, impact, occurrences and fate in the environment. Environment health and risk assessment tools that are used to evaluate the harmfulness, exposure of living organisms to pollutants and the amount of pollutant accumulated are explained with help of bio-kinetic models. Biotransfer, toxicity factor, biomagnification and bioaccumulation of different pollutants in the air, water and marine ecosystems are critically addressed. Thus, the presented survey would be collection of correlations those addresses the factors involved in assessing the environmental health and risk impacts of distinct environmental pollutants.

Temporal and regional variability of cumulative ecological risks of pesticides in Japanese river waters for 1990-2010

We quantitatively evaluated the cumulative ecological risks from multiple pesticides used in paddy fields in Japan. Moreover, we visualized the temporal and regional variability of those risks for 1990-2010. Considering the region-specific parameters of environmental conditions, region-specific predicted environmental concentrations were estimated at 350 river-flow monitoring sites in Japan. Then the multi-substance potentially affected fraction (msPAF) was calculated as a risk index of multiple pesticides by using the computation tool NIAES-CERAP. The median msPAF values for insecticides and herbicides decreased by 92.4% and 53.1%, respectively, from 1990 to 2010. This substantial reduction in ecological risk was attributed to the development of low-risk pesticides by manufacturers, the efforts of farmers in risk reduction, and tighter regulation by the Japanese government. In particular, the substantial reduction of the ecological risk from insecticides was largely due to the decrease in the use of organophosphorus insecticides.

Evaluation of interregional consistency in associations between neonicotinoid insecticides and functions of benthic invertebrate communities in rivers in urban rice-paddy areas

Neonicotinoid insecticides pose risks that need to be managed for conservation of aquatic ecosystems. In this study, we evaluated the associations between the estimated environmental concentrations of two neonicotinoid insecticides (imidacloprid and dinotefuran) and the total abundances of seven functional feeding groups (FFGs) of benthic invertebrate communities in rivers in urban rice-paddy areas in four Japanese regions. Regional datasets of benthic invertebrate communities and environmental variables available for Japan were analyzed. The associations between neonicotinoid exposure and benthic functional groups in each region were evaluated by applying a partial redundancy analysis to each regional dataset. We then examined whether there was an interregionally consistent pattern in the observed associations to ascertain the general applicability of the associations. In two of the four regions, the associations of the total abundances of the seven FFGs with neonicotinoid concentrations were significant, suggesting negative effects of imidacloprid and dinotefuran on river ecosystem functions in these two Japanese regions. Moreover, although the associations in the remaining two regions were not significant, the pattern of associations of the total abundances of six of the FFGs (shredders, filter feeders, collectors, grazers, predators, and scavengers) with imidacloprid concentrations seemed to be consistent among the four regions. This implies broad-scale negative effects of imidacloprid on river ecosystem functions in urban rice-paddy areas. We did not, however, find any interregionally consistent patterns in the associations with dinotefuran concentrations. This may be related to the multicollinearity with the imidacloprid concentrations and/or the low maximum dinotefuran concentration relative to the toxicity values of this neonicotinoid. Therefore, the association between dinotefuran and river ecosystem functions requires additional investigation. We believe that this type of hypotheses-generating research using country-wide biomonitoring and exposure databases can be a great aid in future ecological risk assessment studies.

The reproductive toxicity and potential mechanisms of combined exposure to dibutyl phthalate and diisobutyl phthalate in male zebrafish (Danio rerio)

Dibutyl phthalate (DBP) and diisobutyl phthalate (DiBP) are phthalate compounds frequently detected in the environment. Despite increasing awareness of their toxicity in human and animals, the male reproductive toxicity of their combined exposure remains elusive. The purposes of this study were to investigate whether combined exposure to DBP and DiBP could induce male reproductive toxicity, and to explore the potential toxicological mechanisms. Adult male zebrafish were exposed to DBP (11, 113 and 1133 μg L^-1), DiBP (10, 103 and 1038 μg L^-1) and their mixtures (Mix) (11 + 10, 113 + 103, 1133 + 1038 μg L^-1) for 30 days, and their effects on plasma hormone secretion, testis histology and transcriptomics were examined. Highest concentrations of Mix exposure caused greater imbalance ratio of T/E2 and more severe structural damage to testis than single exposure. These effects were consistent with the testis transcriptome analysis for which 4570 genes were differentially expressed in Mix exposure, while 2795 and 1613 genes were differentially expressed in DBP and DiBP, respectively. KEGG pathway analysis showed that both single and combined exposure of DBP and DiBP could affect cytokine-cytokine receptor interaction. The difference was that combined exposure could also affect steroid hormone synthesis, extracellular matrix receptor interaction, retinol metabolism, and PPAR signaling pathways. These results demonstrated that combined exposure to DBP and DiBP could disrupt spermatogenesis and elicit male reproductive toxicity in zebrafish.

Occurrence of neonicotinoids and fipronil in estuaries and their potential risks to aquatic invertebrates

This study aimed to evaluate and qualify field-based potential risks of seven neonicotinoid and phenylpyrazole (fipronil) insecticides on aquatic invertebrates, including estuary-resident marine crustaceans. One hundred and ninety-three estuarine water samples, with salinity ranging from 0.5 to 32.7, were collected from four estuarine sites in the Seto Inland Sea of Japan, in 2015-2018 and the insecticide levels were measured. Five neonicotinoid and fipronil insecticides were successfully identified, and their occurrence varied temporally. Marine crustaceans were simultaneously harvested every month from one of the estuarine water sampling sites in 2015-2017. Three predominant crustacean species, kuruma prawn (Penaeus japonicus), sand shrimp (Crangon uritai), and mysid (Neomysis awatschensis), were captured and their seasonal presence was species independent. A 96-h laboratory toxicity study with the insecticides using kuruma prawn, sand shrimp, and a surrogate mysid species (Americamysis bahia) indicated that fipronil exerted the highest toxicity to the three crustaceans. Using both toxicity data and insecticide occurrence in estuarine water (salinity ≥10, n = 169), the potential risks on the three marine crustaceans were quantified by calculating the proportion of mixture toxicity effects (P_mix). The P_mix of seven neonicotinoids on the crustaceans was less than 0.8%, which is likely to be too low to indicate adverse effects caused by the insecticides. However, short temporal detection of fipronil (exclusively in June and July) significantly affected the P_mix, which presented the maximal P_mix values of 21%, 3.4%, and 72% for kuruma prawn, sand shrimp, and mysid, respectively, indicating a significant effect on the organisms. As for estuarine water (salinity <10), some water samples contained imidacloprid and fipronil exceeding the freshwater benchmarks for aquatic invertebrates. The present study provides novel insights into the seasonally varying risks of insecticides to estuarine crustaceans and highlights the importance of considering whether ecological risk periods coincide with crustacean presence.

Demonstrating the need for chemical exposure characterisation in a microplate test system: toxicity screening of sixteen pesticides on two marine microalgae

Pesticides used in viticulture create a potential risk for the aquatic environment due to drift during application, runoff and soil leaching. The toxicity of sixteen pesticides and one metabolite were evaluated on the growth of two marine microalgae, Tisochrysis lutea and Skeletonema marinoi, in 96-h exposure assays conducted in microplates. For each substance, concentrations of stock solutions were analytically measured and abiotic assays were performed to evaluate the chemical stability of pesticides in microplates. For two chemicals, microalgae exposures were run simultaneously in microplates and culture flasks to compare EC₅₀ calculated from the two exposure systems. Results from chemical analyses demonstrated the low stability of hydrophobic pesticides (log K_OW > 3). For such chemicals, EC₅₀ values calculated using measured pesticide concentrations were two-fold lower than those first estimated using nominal concentrations. Photosystem II inhibitors were the most toxic herbicides, with EC₅₀ values below 10 μg L^-1 for diuron and around double this for isoproturon. Chlorpyrifos-methyl was the only insecticide to significantly affect the growth of T. lutea, with an EC₅₀ around 400 μg L^-1. All fungicides tested were significantly toxic to both species: strobilurins showed low overall toxicity, with EC₅₀ values around 400 μg L^-1, whereas quinoxyfen, and spiroxamine, showed high toxicity to both species, especially to T. lutea, with an EC₅₀ below 1 μg L^-1 measured for spiroxamine in culture flasks. This study highlights the need to perform chemical analyses for reliable toxicity assessment and discusses the advantages and disadvantages of using microplates as a toxicity screening tool.

Combined toxicity of endosulfan and phenanthrene mixtures and induced molecular changes in adult Zebrafish (Danio rerio)

Individual and combined toxicities of endosulfan (ENDO) with phenanthrene (PHE) were evaluated using zebrafish (Danio rerio) adults. The 96-h LC₅₀ values for ENDO and PHE were 4.6 μg L^-1 and 920 μg L^-1, respectively. To evaluate the mixture toxicity, LC₁₀ and LC₅₀ concentrations were grouped into four combinations as ENDO-LC₁₀ + PHE-LC₁₀, ENDO-LC₁₀ + PHE-LC₅₀, ENDO-LC₅₀ + PHE-LC₁₀, and ENDO-LC₅₀ + PHE-LC₅₀, and their acute toxicities were determined. The combination of LC₅₀-ENDO and LC₁₀-PHE exhibited a synergistic effect. In addition, acetylcholinesterase activity decreased in zebrafish bodies exposed to ENDO with or without PHE. Combined treatments induced higher glutathione S-transferase activity compared to individual treatments. Carboxylesterase activity increased in both heads and bodies of ENDO-treated fishes compared with PHE-treated fishes. Using RT-qPCR technique, CYP1A gene expression significantly up-regulated in all combinations, whereas CYP3A was unchanged, suggesting that enzymes involved in defense may play different roles in the detoxification. CYP7A1 gene responsible for bile acid biosynthesis is dramatically down-regulated after exposure to the synergistic combination exposure, referring that the synergistic effect may be resulted from the reduction of bile production in zebrafishes. Among gender-related genes, CYP11A1 and CYP17A1 genes in female zebrafish decreased after treatment with ENDO alone and combination of LC₅₀-ENDO and LC₁₀-PHE. This might be related to a reduction in cortisol production. The overall results indicated that ENDO and PHE were toxic to zebrafish adults both individually and in combination, and that their co-presence induced changes in the expression of genes responsible for metabolic processes and defense mechanisms.