Multigenerational exposure of populations of Oppia nitens to zinc under pulse and continuous exposure scenarios

Effect of Insecticide Exposure Across Multiple Generations of the Earthworm Eisenia andrei

The toxicity of neonicotinoids and many of their replacement insecticides to nontarget soil invertebrates such as earthworms has previously been established. However, the long-term effects of these substances on these organisms are largely unknown. In the field of soil ecotoxicology, lumbricid earthworms such as Eisenia andrei are used extensively due to the availability of standardized test methods and their adaptability to laboratory culture and testing. Multigenerational studies have gained popularity and attention in recent years, with a shift toward the use of long-term assays and lower concentrations of test chemicals. The use of exposure concentrations that include those measured in a monitoring program carried out by the Government of Ontario presents a realistic exposure scenario that may not show significant effects in contemporary, shorter term studies. We used current standardized test methods as a basis for the development of multigenerational studies on E. andrei. The effects of exposure to a single application of the insecticides thiamethoxam and cyantraniliprole on the survival and reproduction of E. andrei were observed over three (thiamethoxam) or two (cyantraniliprole) generations using consecutive reproduction tests. No significant impacts on adult survival were reported in any generation for either insecticide, whereas reproduction decreased between the first and second generations in the thiamethoxam test, with median effective concentration (EC50) values of 0.022 mg/kg dry weight reported for the first generation compared with 0.002 mg/kg dry weight in the second generation. For cyantraniliprole, an EC50 of 0.064 was determined for the first generation compared with 0.016 mg/kg dry weight in the second generation. A third generation was completed for the thiamethoxam test, and a significant decrease in reproduction was observed in all treatments and controls compared with previous generations. No significant difference between thiamethoxam treatments and the control treatment was reported for the third generation. Collectively, these data indicate that exposure of oligochaetes to these two insecticides at concentrations representative of field conditions may result in long-term stresses. Environ Toxicol Chem 2024;00:1-13. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Integument colour change: Tracking delayed growth of Oppia nitens as a sub-lethal indicator of soil toxicity

Growth is an important toxicity end-point in ecotoxicology but is rarely used in soil ecotoxicological studies. Here, we assessed the growth change of Oppia nitens when exposed to reference and heavy metal toxicants. To assess mite growth, we developed an image analysis methodology to measure colour spectrum changes of the mite integument at the final developmental stage, as a proxy for growth change. We linked the values of red, green, blue, key-black, and light colour of mites to different growth stages. Based on this concept, we assessed the growth change of mites exposed to cadmium, copper, zinc, lead, boric acid, or phenanthrene at sublethal concentrations in LUFA 2.2 soil for 14 days. Sublethal effects were detected after 7 days of exposure. The growth of O. nitens was more sensitive than survival and reproduction when exposed to copper (EC50growth = 1360 mg/kg compared to EC50reproduction = 2896 mg/kg). Mite growth sensitivity was within the same order of magnitude to mite reproduction when exposed to zinc (EC50growth = 1785; EC50reproduction = 1562 mg/kg). At least 25% of sublethal effects of boric acid and phenanthrene were detected in the mites but growth was not impacted when O. nitens were exposed to lead. Consistent with previous studies, cadmium was the most toxic metal to O. nitens. The mite growth pattern was comparable to mite survival and reproduction from previous studies. Mite growth is a sensitive toxicity endpoint, ecologically relevant, fast, easy to detect, and can be assessed in a non-invasive fashion, thereby complimenting existing O. nitens testing protocols.

Influences of continuous and pulse atrazine exposure on intestinal flora and metabolites of Pelophylax nigromaculatus tadpoles

Atrazine, a widely used herbicide, has adverse effects on the growth and metabolism of amphibians. Due to the cyclical application use of the pesticide atrazine in agricultural production, atrazine concentrations in water occur in the form of pulses. However, knowledge of the effects of atrazine pulse exposure on the gut microbiota and metabolism of amphibians is limited. In this study, Pelophylax nigromaculatus tadpoles (Gs 26) were exposed to continuous and pulse atrazine (100 μg/L) for 60 days. The results showed that continuous exposure and pulse exposure had different effects on the diversity of gut microbiota. At the phyla level, pulse exposure significantly increased the relative abundance of Actinobacteria, and decreased the relative abundance of Firmicutes compared to continuous exposure. At the genus level, continuous and pulse exposure to atrazine significantly altered the relative abundance of Acetobacterium, Microbacterium, Bacteroides, Eulopiscium and Leuconostoc. Compared to continuous exposure, pulse exposure significantly increased the relative abundance of Microbacterium, and significantly decreased the relative abundance of Acetobacterium and Eplopiscium. In terms of metabolism, pulse exposure significantly increased the relative abundance of creatine, guanine, and inosine and significantly decreased the relative abundance of 3-hydroxysebacic acid, ganoderic acid F, hypoxanthine, and withaperuvin H compared to continuous exposure. Continuous and pulse exposure to atrazine significantly altered the relative abundance of metabolites of the pymidine metabolism, purine metabolism, beta-alanine metabolism and other pathways in the gut of P. nigromaculatus tadpoles. In addition, changes in most metabolites had a significant correlation with changes in gut microorganisms. In conclusion, our study confirmed that pulse exposure to atrazine has a greater effect on the composition of the gut microflora and the metabolism of P. nigromaculatus tadpoles than continuous exposure.

On the importance of longer-term exposure to stressors - A critical review and proposal for multigenerational testing in standard soil invertebrates

Standard laboratory tests to describe the impact of stressors (most notably: chemicals) on organisms offer a good compromise between feasibility and outcome, i.e., they should be reproducible and provide robust results. However, these tests may underestimate the potential effects of prolonged exposures, particularly for persistent contaminants. Within the last years, we have observed an increase in studies aiming to target prolonged exposure, e.g., via an extended test duration or by multigenerational (MG) exposure. Seemingly, both reduced and increased impacts have been observed in these studies, but it is also clear that no unique test setup was used, and test designs vary widely among studies. To better describe long term effects, MG is a highly relevant aspect which deserves more consideration at various testing and assessment levels. Therefore, we conducted a literature review focusing on available studies performed with soil invertebrates, exposed to stressors for periods longer than in standard laboratory tests, i.e., full life cycle tests, as well as extensions to standard and MG tests. So far, it has been recommended that such studies should cover more than one generation, but this statement is probably too vague. In this contribution, we summarize and critically discuss the information provided in the literature, and we provide suggestions for future research. The currently available test results from long-term studies have produced clear evidence to recommend the implementation of long-term tests in existing regulatory testing requirements (e.g., for pesticides), in particular for persistent substances and also for delayed effects. Consequently, we recommend the inclusion of such longer exposure test designs (e.g., as annexes) in current OECD and ISO guidelines. However, when doing so, the long-term test designs proposed so far have to be critically adapted for a selected set of representative soil invertebrate test species.

Effects of short-term continuous and pulse cadmium exposure on gut histology and microbiota of adult male frogs (Pelophylax nigromaculatus) during pre-hibernation

Cadmium (Cd) is an environmental endocrine-disrupting pollutant which mainly occurs in pulsed manner in natural waters, while traditional toxicology experiments have less examined the effects of pulsed exposure. Here, we studied the effects of short-term (7 days) continuous and pulse exposure to 100 μg/L Cd on gut morphology and microbiota of frogs (Pelophylax nigromaculatus) during pre-hibernation. Compared to continuous exposure, Cd pulse exposure significantly increased individual mortality and decreased the villi height and the ratio of villi height to crypt depth of the gut. Cd continuous and pulse exposure both changed the community structure and relative abundance of intestinal microbiota. Compared to continuous exposure, Cd pulse exposure significantly decreased the relative abundance of beneficial bacteria (e.g., Cetobacterium and Aeromonas genus), and significantly increased the relative abundance of harmful bacteria (e.g., Parabacteroides, Odoribacter, and Acinetobacter genus). This study shows that the gut histology and microbiota of amphibians during pre-hibernation are more susceptible to Cd pulse exposure than continuous exposure.

Multigeneration toxicity of Geunsami® (a glyphosate-based herbicide) to Allonychiurus kimi (Lee) (Collembola) from sub-individual to population levels

Glyphosate-based herbicide (GBH) is the most widely used herbicide worldwide and has long been considered to have significantly low toxicity to non-target soil invertebrates based on short-term toxicity tests (<56 d). However, long-term GBH toxicity assessment is necessary as GBH is repeatedly applied in the same field annually because of the advent of glyphosate-resistant crops. In this study, a multigeneration test was conducted where Allonychiurus kimi (Collembola) was exposed to GBH for three generations (referred to as F0, F1, and F2) to evaluate the long-term toxic effect. The endpoints used were adult survival and juvenile production for the individual level toxicity assessment. Phospholipid profile and population age structure were the endpoints used for sub-individual and population levels, respectively. GBH was observed to have no negative effects on adult survivals of all generations, but juvenile production was found to decrease in a concentration-dependent manner, with EC50s being estimated as 572.5, 274.8, and 59.8 mg a.i. kg-1 in the F0, F1, and F2 generations, respectively. The age structure of A. kimi population produced in the test of all generations was altered by GBH exposure, mainly because of the decrease in the number of young juveniles. Further, differences between the phospholipid profiles of the control and GBH treatments became apparent over generations, with PA 16:0, PA 12:0, and PS 42:0 lipids not being detected at the highest concentration of 741 mg kg-1 in F2. Considering all our findings from sub-individual to population levels, repeated and long-term use of GBH could have significantly higher negative impacts on non-target soil organisms than expected.

Effects of continuous and intermittent cadmium exposure on HPGL axis, GH/IGF axis and circadian rhythm signaling and their consequences on reproduction in female zebrafish: Biomarkers independent of exposure regimes

Typical biomarkers of cadmium (Cd) pollution have well been confirmed in fish from continuous exposure pattern. However, in a natural environment, fish may be exposed to Cd intermittently. In this study, juvenile female zebrafish were exposed for 48 days to 10 μg/L Cd continuously, 20 μg/L for 1 day in every 2 days or 30 μg/L for 1 day in every 3 days. The toxic effects were evaluated using 8 various physiological and biochemical endpoints like specific growth rate (SGR), 17β-estradiol (E2) and vitellogenin (VTG) concentrations in plasma, reproductive parameters (gonadosomatic index (GSI), egg-laying amount, spawning percentage, and hatching and mortality rate of embryos). Transcription of 59 genes related to hypothalamic-pituitary-gonadal-liver (HPGL) axis, circadian rhythm signaling and insulin-like growth factor (IGF) system was examined. SGR, spawning percentage, E2 and VTG levels declined in fish exposed to 10 and 20 μg/L Cd but remained relatively stable in fish exposed to 30 μg/L Cd. Exposure to 10, 20 and 30 μg/L Cd significantly reduced GSI, hatching rate and mortality rate. Similarly, mRNA expression of 27 genes were sensitive to both continuous and intermittent Cd exposure. Among these genes, expression levels of 10 genes had more than 5-fold increase or decrease, including mRNA levels of vtg1, vtg2, vtg3, esr1, igf2a, igf2b, igfbp5b, nr1d1, gnrh3 and gnrhr4. The most sensitive molecular biomarker was vtg3 expression with 1500-3100 fold increase in the liver. The present study, for the first time, provides effective candidate biomarkers for Cd, which are independent of exposure regimes.

Assessment of the risk of death of Clarias gariepinus and Oreochromis niloticus pulse-exposed to selected agricultural pesticides

Aquatic organisms are often exposed briefly to high pesticide concentration. Survival time model was used to study risk of death in C. gariepinus and O. niloticus fingerlings exposed to 24 mg/L atrazine, 42 mg/l mancozeb, 1 mg/L chlorpyrifos and 0.75 µg/L lambda cyhalothrin for 15, 30, 45 and 60 minutes and continuously for 96 hours. Mortality, time-to-death, weight, length, and condition factor of the fingerlings were recorded. Results obtained showed tilapia was more susceptible than catfish to continuous exposure but not pulse exposure. The survival probability of both species was similar when exposed for 15, 30 and 45 minutes (p > 0.05) but differed after 60 minutes (p < 0.05). Risk of death of catfish exposed briefly to atrazine, mancozeb and chlorpyrifos for 60 minutes was similar to 96 hours continuous exposure, same for tilapia exposed to 1 mg/L chlorpyrifos (p > 0.05). Survival probability of tilapia exposed to chlorpyrifos for 15, 30, 45 and 60 minutes was similar (p > 0.05) and was not influenced by pulse length. Pesticide hazard and risk of death decreased as fish size (weight, length, and condition factor) increased. Pulse toxicity assessment using survival models could make pesticides exposure assessment more realistic by studying factors that can influence the toxicity of pesticides.

Paternal multigenerational exposure to an obesogenic diet drives epigenetic predisposition to metabolic diseases in mice

Obesity is a growing societal scourge. Recent studies have uncovered that paternal excessive weight induced by an unbalanced diet affects the metabolic health of offspring. These reports mainly employed single-generation male exposure. However, the consequences of multigenerational unbalanced diet feeding on the metabolic health of progeny remain largely unknown. Here, we show that maintaining paternal Western diet feeding for five consecutive generations in mice induces an enhancement in fat mass and related metabolic diseases over generations. Strikingly, chow-diet-fed progenies from these multigenerational Western-diet-fed males develop a 'healthy' overweight phenotype characterized by normal glucose metabolism and without fatty liver that persists for four subsequent generations. Mechanistically, sperm RNA microinjection experiments into zygotes suggest that sperm RNAs are sufficient for establishment but not for long-term maintenance of epigenetic inheritance of metabolic pathologies. Progressive and permanent metabolic deregulation induced by successive paternal Western-diet-fed generations may contribute to the worldwide epidemic of metabolic diseases.

Effect of long-term exposure to copper on survival and development of two successive generations of Culex pipiens (Diptera, Culicidae)

Aquatic invertebrates can be exposed to copper from various sources, including agricultural applications. For example, concentrations up to 1000 µg L^-1 are found within rice fields, where copper-containing formulations are used as fungicides and algaecides. We conducted toxicity tests to study lethal and sublethal effects of copper sulfate pentahydrate on all immature stages across two generations of Culex pipiens mosquitoes as our model organism. Mortality was dose-dependent at concentrations of 500 µg L^-1 and above in the first generation, and 125 µg L^-1 and above in the second generation. The median lethal concentrations (LC₅₀) of copper sulfate pentahydrate for larval Cx. pipiens were 476 ± 30.60 µg L^-1 and 348.67 ± 23.20 µg L^-1 for the first and second generations, respectively. Generation one pupation decreased from 96% in controls to 48% at 500 µg L^-1, while the second-generation pupation decreased from 96% in controls to 17.5% at 500 µg L^-1. Mortality during the pupal stage varied from 2 to 10% at 500 µg L^-1 of first and second generations, respectively. Higher levels also delayed development to adulthood in both generations. The duration of the immature period was 14.8 days in controls in both generations, but when exposed at 500 µg L^-1 it increased to 18.8 days in the first generation and to 20.5 days in the second generation. The chronic, multi-generation exposures in this study showed greater toxicity than reported for shorter exposures of Cx. pipiens, and confamilial taxa like Culex hortensis and Anopheles hispaniola.

Single metal and metal mixture toxicity of five metals to Oppia nitens in five different Canadian soils

Metal mixture toxicity across soil types is a daunting challenge to risk assessment. Here, we evaluated metal mixture toxicity in Oppia nitens, using ten fixed metal mixture ratios in five Canadian soils that closely matched some of the EU PNEC reference soils. Soils were dosed with five metals (Cu, Zn, Pb, Co, Ni) as single metals (ten concentrations) and as mixtures (eight concentrations). Synchronized adult mites were exposed to metals, with survival and reproduction assessed after 28 days. We found out that (i) the differences among soils in mite sensitivity and single metals were not consistent when mites were exposed to metal mixtures, (ii) assuming concentration addition, the mixture interaction factor (MIF) showed that single metal low effect levels excessively underestimated low level metal mixture effects (iii) Zn emerged as a protective metal in most mixtures, and (iv) Soil properties such as CEC, independent of effects on metal speciation, explained more of the variation than measured metals. This study suggests that metal risk assessment should be done on a case by case basis. Further work is needed to ensure that by protecting soil-dwelling organisms from single metals, the risk from metal mixtures is appropriately protected for.

Uptake, toxicity, and maternal transfer of cadmium in the oribatid soil mite, Oppia nitens: Implication in the risk assessment of cadmium to soil invertebrates

Cadmium (Cd) is a heavy metal of concern in contaminated sites because of its high toxicity to soil biota and humans. Typically, Cd exposure is thought to be dominated by dissolved Cd in soil pore water and, thus, dermal uptake. In this study, we investigated the uptake, toxicity, and maternal transfer of Cd in a standard soil invertebrate, the oribatid mite (Oppia nitens), which is common to boreal and temperate ecozones. We found total soil Cd predicted Cd uptake in adult and juvenile O. nitens with no significant uptake from pore water by juvenile mites. Cadmium significantly inhibited juvenile production and recruitment as well as reduced adult fecundity. Adult O. nitens maternally transferred 39-52% of their Cd body burden to juveniles (tritonymphs) while the maternally-acquired Cd accounted for 41% of the juvenile internal Cd load. Our results suggest that dermal adsorption of metal ions is not important for O. nitens and that maternal transfer of Cd in soil invertebrates has ecological and toxicological implications for populations of soil invertebrates. Maternal transfer should be incorporated as a criterion in setting environmental soil quality guidelines (SQG_E) for cadmium and other non-essential heavy metals.

Oppia nitens C.L. Koch, 1836 (Acari: Oribatida): Current Status of Its Bionomics and Relevance as a Model Invertebrate in Soil Ecotoxicology

The oribatid soil mite Oppia nitens C.L. Koch, 1836, is a model microarthropod in soil ecotoxicity testing. This species has a significant role in supporting soil functions and as a suitable indicator of soil contamination. Despite its significance to the environment and to ecotoxicology, however, very little is known of its biology, ecology, and suborganismal responses to contaminants in the soil. In the present review, we present detailed and critical insights into the biology and ecology of O. nitens in relation to traits that are crucial to its adaptive responses to contaminants in soil. We used a species sensitivity distribution model to rank the species sensitivity to heavy metals (cadmium and zinc) and neonicotinoids (imidacloprid and thiacloprid) compared with other standardized soil invertebrates. Although the International Organization for Standardization and Environment and Climate Change Canada are currently standardizing a protocol for the use of O. nitens in soil toxicity testing, we believe that O. nitens is limited as a model soil invertebrate until the molecular pathways associated with its response to contaminants are better understood. These pathways can only be elucidated with information from the mites' genome or transcriptome, which is currently lacking. Despite this limitation, we propose a possible molecular pathway to metal tolerance and a putative adverse outcome pathway to heavy metal toxicity in O. nitens. Environ Toxicol Chem 2019;38:2593-2613. © 2019 SETAC.

The forgotten role of toxicodynamics: How habitat quality alters the mite, Oppia nitens, susceptibility to zinc, independent of toxicokinetics

Soil habitat quality is thought to influence metal toxicity via changes in speciation and thereby toxicokinetics. Here, we assessed the toxicokinetic and toxicodynamic effects of habitat quality on mite, Oppia nitens when exposed to zinc (Zn) contaminated soils. Forty-seven soils were ranked into three habitat qualities; high, medium, and low based on biological reproduction of Folsomia candida, Enchytraeus crypticus, and Elymus lanceolatus. From the 47 soils, eighteen soils (comprising of six soils from each habitat quality) were randomly selected and dosed with field relevant concentrations of Zn. Mite survival and reproduction were assessed after 28 days. Total Zn, bioaccessible Zn, Zn bioavailability, Zn body burden, lactate dehydrogenase activity (LDH) and glucose-6-phosphate dehydrogenase (G6PDH) activities of the mites were determined. Zinc toxicity and potency were much less in the high compared to low quality soils and the mites in the high habitat quality soils tolerated higher zinc body burdens (2040 ± 130 μg/g b.w) than the lower habitat quality (1180 ± 310 μg/g b.w). Lower LDH activity (20 ± 2 μU mg^-1) in the high quality soils compared to lower quality soils (50 ± 8 μU mg^-1) suggested that there was less stress in the high habitat quality mites. Despite changes in speciation across habitat qualities, bioavailability of zinc was similar (∼20%) irrespective of habitat quality. Our results suggest that the influence of soil properties on survival is modulated by toxicodynamics rather than toxicokinetics. Restoring habitat quality may be more important for soil invertebrate protection than metal concentration at contaminated sites.

Predicting the survival of zebrafish larvae exposed to fluctuating pulses of lead and cadmium

Aquatic organisms are often exposed to time-varied concentrations of contaminants due to pulsed inputs in natural water. Traditional toxicology experiments are usually carried out in a constant exposure pattern, which is inconsistent with the actual environment. In this study, a refined toxicokinetic-toxicodynamic (TK-TD) model was used to study the toxic effects of Pb and Cd on zebrafish larvae under three pulse exposures with 2, 4, and 6 h, respectively. The parameter sensitivity analysis showed that J_{M, max} had the greatest impact on the output of the model. Cd or Pb pulse exposure resulted in less death than constant exposure at the same time-weighted average (TWA) concentrations. Survival fraction in larvae under 6 h interval between two pulses of Pb or Cd was larger than that under 2 h and 4 h interval. Toxicity under constant exposure of Cd or Pb was greater than that under 2, 4, and 6 h interval pulse exposure because the cumulative Cd or Pb concentration in the body under constant exposure was greater than that under pulse exposure. The results also showed that the stochastic death (SD) model was more suitable than the individual tolerance (IT) model for predicting the survival fraction of larvae under pulse exposure to Pb and Cd, which was indicated by higher R² (0.670-0.940) in SD model than that (0.588-0.861) in IT model. Our model provides approaches for laboratory toxicity testing and modeling approaches for addressing the toxicity of heavy metal pulsed exposure.