Influence of feeding and earthworm density on compound bioaccumulation in earthworms Eisenia andrei

Earthworm lipid content and size help account for differences in pesticide bioconcentration between species

The uptake and elimination kinetics of pesticides from soil to earthworms are important in characterising the risk of pesticides to soil organisms and the risk from secondary poisoning. However, the understanding of the relative importance of chemical, soil, and species differences in determining pesticide bioconcentration into earthworms is limited. Furthermore, there is insufficient independent data in the literature to fully evaluate existing predictive bioconcentration models. We conducted kinetic uptake and elimination experiments for three contrasting earthworm species (Lumbricus terrestris, Aporrectodea caliginosa, Eisenia fetida) in five soils using a mixture of five pesticides (log Kow 1.69 - 6.63). Bioconcentration increased with pesticide hydrophobicity and decreased with soil organic matter. Bioconcentration factors were comparable between earthworm species for hydrophilic pesticides due to the similar water content of earthworm species. Inter-species variations in bioconcentration of hydrophobic pesticides were primarily accounted for by earthworm lipid content and specific surface area (SSA). Existing bioconcentration models either failed to perform well across earthworm species and for more hydrophilic compounds (log Kow < 2) or were not parameterised for a wide range of compounds and earthworm species. Refined models should incorporate earthworm properties (lipid content and SSA) to account for inter-species differences in pesticide uptake from soil.

Chlorine substitution-dependent toxicities of polychlorinated biphenyls to the earthworm Eisenia fetida in soil

Polychlorinated biphenyls (PCBs) with different chlorine substitution patterns often coexist in e-waste-processing sites. However, the single and combined toxicity of PCBs to soil organisms and the influence of chlorine substitution patterns remain largely unknown. Herein, we evaluated the distinct in vivo toxicity of PCB28 (a trichlorinated PCB), PCB52 (a tetrachlorinated PCB), PCB101 (a pentachlorinated PCB), and their mixture to earthworm Eisenia fetida in soil, and looked into the underlining mechanisms in an in vitro test using coelomocytes. After a 28-days exposure, all PCBs (up to 10 mg/kg) were not fatal to earthworms, but could induce intestinal histopathological changes and microbial community alterations in the drilosphere system, along with a significant weight loss. Notably, pentachlorinated PCBs with a low bioaccumulation ability showed greater inhibitory effects on the growth of earthworm than lowly chlorinated PCBs, suggesting that bioaccumulation was not the main determinant of chlorine substitution-dependent toxicity. Furthermore, in vitro assays showed that the highly chlorinated PCBs induced a high-percentage apoptosis of eleocytes in the coelomocytes and significantly activated antioxidant enzymes, indicating that the distinct cellular vulnerability to lowly/highly chlorinated PCBs was the main contributor to the PCBs toxicity. These findings emphasize the specific advantage of using earthworms in the control of lowly chlorinated PCBs in soil due to their high tolerance and accumulation ability.

Insights into the mechanisms of organic pollutant toxicity to earthworms: Advances and perspectives

Earthworms play positive ecological roles in soil formation, structure, and fertility, environmental protection, and terrestrial food chains. For this review, we searched the Web of Science database for articles published from 2011 to 2021 using the keywords "toxic" and "earthworm" and retrieved 632 publications. From the perspective of bibliometric analysis, we conducted a co-occurrence network analysis using the keywords "toxic" and "earthworm" to identify the most and least reported topics. "Eisenia fetida," "bioaccumulation," "heavy metals," "oxidative stress," and "pesticides" were the most common terms, and "microbial community," "bacteria," "PFOS," "bioaugmentation," "potentially toxic elements," "celomic fluid," "neurotoxicity," "joint toxicity," "apoptosis," and "nanoparticles" were uncommon terms. Additionally, in this review we highlight the main routes of organic pollutant entry into soil, and discuss the adverse effects on the soil ecosystem. We then systematically review the mechanisms underlying organic pollutant toxicity to earthworms, including oxidative stress, energy and lipid metabolism disturbances, neurological toxicity, intestinal inflammation and injury, gut microbiota dysbiosis, and reproductive toxicity. We conclude by discussing future research perspectives, focusing on environmentally relevant concentrations and conditions, novel data processing approaches, technologies, and detoxification and mitigation methods. This review has implications for soil management in the context of environmental pollution.

Toxicokinetics of hydrophobic organic compounds in oligochaeta: A critical review

Toxicokinetic studies appertain to the fundamental research of soil bioavailability. However, the research outcomes of aspects influencing uptake and elimination of hydrophobic organic compounds have not been summarized so far. In our review, a recapitulation of available toxicokinetic data (i.e. experimental conditions, if the steady state was reached, uptake and elimination rate constants, and bioaccumulation factors) is presented in well-arranged tables. Further, toxicokinetic models are overviewed in the schematic form. In the review, the required information could be quickly found and/or the experimental gaps easily identified. Generally a little is known about the effects of soil properties other than soil organic matter. Limited or no data are available about soil treatment, food supply during laboratory exposure, and metabolization in oligochaeta. The impact of these factors might be important especially for arable soils with typically low organic matter content but high consequences on humans. Besides these circumstances, other uncertainties between published studies have been found. Firstly, the scientific results are provided in heterogenous units: bioaccumulation factors as well as the rate constants are reported in dry or wet weight of soil and earthworms. The steady state is another critical factor because the time to reach the equilibrium is influenced not only by soil and compound characteristics but for example also by aging. Nevertheless, toxicokinetic studies bring irreplaceable information about the real situation in soil and our review help to define missing knowledge and estimate the scientific priorities.

Accumulation of Insensitive Munition Compounds in the Earthworm Eisenia andrei from Amended Soil: Methodological Considerations for Determination of Bioaccumulation Factors

The present study investigates the bioaccumulation of the insensitive munition compounds 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO), developed for future weapons systems to replace current munitions containing sensitive explosives. The earthworm Eisenia andrei was exposed to sublethal concentrations of DNAN or NTO amended in Sassafras sandy loam. Chemical analysis indicated that 2- and 4-amino-nitroanisole (2-ANAN and 4-ANAN, respectively) were formed in DNAN-amended soils. The SumDNAN (sum of DNAN, 2-ANAN, and 4-ANAN concentrations) in soil decreased by 40% during the 14-d exposure period. The SumDNAN in the earthworm body residue increased until day 3 and decreased thereafter. Between days 3 and 14, there was a 73% decrease in tissue uptake that was greater than the 23% decrease in the soil concentration, suggesting that the bioavailable fraction may have decreased over time. By day 14, the DNAN concentration accounted for only 45% of the SumDNAN soil concentration, indicating substantial DNAN transformation in the presence of earthworms. The highest bioaccumulation factor (BAF; the tissue-to-soil concentration ratio) was 6.2 ± 1.0 kg/kg (dry wt) on day 3 and decreased to 3.8 ± 0.8 kg/kg by day 14. Kinetic studies indicated a BAF of 2.3 kg/kg, based on the earthworm DNAN uptake rate of 2.0 ± 0.24 kg/kg/d, compared with the SumDNAN elimination rate of 0.87 d^-1 (half-life = 0.79 d). The compound DNAN has a similar potential to bioaccumulate from soil compared with trinitrotoluene. The NTO concentration in amended soil decreased by 57% from the initial concentration (837 mg NTO/kg dry soil) during 14 d, likely due to the formation of unknown transformation products. The bioaccumulation of NTO was negligible (BAF ≤ 0.018 kg/kg dry wt). Environ Toxicol Chem 2021;40:1713-1725. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

The dual beneficial effects of vermiremediation: Reducing soil bioavailability of cadmium (Cd) and improving soil fertility by earthworm (Eisenia fetida) modified by seasonality

This study aimed to assess earthworm's capability of reducing the bioavailability of cadmium (Cd) in soil and increasing soil fertility with the modification of seasonal variations of ambient temperatures on the efficacy of vermiremediation. Earthworms were exposed in soil fortified with 0, 5, 10, and 20 mg Cd kg^-1, for 7, 14 and 21 days in winter and spring. The bioavailability of Cd in soil, which is represented in the form of diethylenetriaminepentaacetic acid-extractable fraction (DTPA-Cd), were significantly reduced, ranging from 7.9 to 18.3% in winter and 8.8 to 20.8% in spring. Meanwhile, we found earthworm activities could significantly improve the soil fertility as the results of increasing the availability of nitrogen, phosphorous, and potassium in soil, a prominent advantage of vermiremediation in heavy metal-contaminated soil. Although seasonality could increase Cd toxicity in earthworms, higher ambient temperature in spring season also promoted the reduction of Cd bioavailability and the increase of soil fertility, due to significant increase of microbial populations. In conclusion, we reported the dual beneficial effects of vermiremediation in reducing bioavailability of Cd in soil and simultaneously improving soil fertility in which both outcomes were modified by seasonality.

Uptake kinetics of four hydrophobic organic pollutants in the earthworm Eisenia andrei in aged laboratory-contaminated natural soils

Laboratory studies of pollutant uptake kinetics commonly start shortly after experimental soil contamination when it is not clear if the processes between soil and chemicals are equilibrated and stabilized. For instance, when the concentration in soil quickly decreases due to initial biodegradation, bioaccumulation may show a peak-shape accumulation curve instead of conventional first order kinetics with a plateau at the end. The results of such experiments with soil freshly contaminated in the laboratory are then hardly comparable to bioaccumulation observed in soils from historically contaminated sites. Therefore, our study focused on the uptake kinetics of four hydrophobic organic compounds (pyrene, lindane, p,p'-DDT and PCB 153) in two laboratory-contaminated natural soils with different soil properties (e.g. total organic carbon content of 1.6 and 9.3%) aged for 203 days to mimic long-term contamination. For pyrene, the results surprisingly showed peak-shape accumulation curves despite long aging. It seems compound biodegradation might be significant in aged soils when the conditions change (e.g. by distribution to the experimental vessels) and this should be also considered when testing historically contaminated soils. For lindane, longer aging seems to guarantee stability of the soil-compound-earthworm system and the steady state was reached after 5 days of exposure. Furthermore, although concentrations of p,p'-DDT and PCB 153 in earthworms after 11-15-day exposure did not statistically differ, which is a commonly-used indicator that a steady state was reached, they continuously increased until the end of the exposure. Therefore, despite the aging, longer exposure was probably needed to reach the true equilibrium between concentrations in earthworms and soil. In summary, aging does not warranty the conventional first order kinetic curve with the equilibrium at the end of the exposure but may have diverse effects for compounds with different environmental properties and should be taken into account in the bioaccumulation factor calculation and the risk assessment.

Uptake, elimination and biotransformation of N-ethyl perfluorooctane sulfonamide (N-EtFOSA) by the earthworms (Eisenia fetida) after in vivo and in vitro exposure

N-ethyl perfluorooctane sulfonamide (N-EtFOSA) is commonly known as the active ingredient of sulfluramid. It can be degraded to perfluorooctane sulfonic acid (PFOS) in biota and environment. Earthworms (Eisenia fetida) were exposed with N-EtFOSA to examine the bioaccumulation, elimination and metabolism of N-EtFOSA by the earthworms after in vivo and in vitro exposure. N-EtFOSA could be biodegraded in quartz sands to perfluorooctane sulfonamide (FOSA) and PFOS. In the in vivo tests, in addition to parent N-EtFOSA, three metabolites, including perfluorooctane sulfonamide acetate (FOSAA), FOSA and PFOS also accumulated in earthworms as a result of N-EtFOSA biotransformation, with FOSA as the predominant metabolite. The bioaccumulation factor (BAF) and uptake rate coefficient (k_u) of N-EtFOSA from sand were 20.4 and 2.41·d^-1, respectively. The elimination rate constants (k_e) decreased in the order FOSAA (0.130·d^-1) > N-EtFOSA (0.118·d^-1) > FOSA (0.073·d^-1) > PFOS (0.051·d^-1). The biotransformation of N-EtFOSA in earthworm was further confirmed by the in vitro test involving incubation of earthworm homogenates with N-EtFOSA. This work provides evidence on the accumulation and transformation of N-EtFOSA in terrestrial invertebrates and will be helpful to explore the indirect sources of FOSA and PFOS in environmental biota.

Combined effects of four pesticides and heavy metal chromium (Ⅵ) on the earthworm using avoidance behavior as an endpoint

In natural ecosystems, organisms are commonly exposed to chemical mixtures rather than individual compounds. However, environmental risk is traditionally assessed based on data of individual compounds. In the present study, we aimed to investigate the individual and combined effects of four pesticides [fenobucarb (FEN), chlorpyrifos (CPF), clothianidin (CLO), acetochlor (ACE)] and one heavy metal chromium [Cr(Ⅵ)] on the earthworm (Eisenia fetida) using avoidance behavior as an endpoint. Our results indicated that CLO had the highest toxicity to E. fetida, followed by Cr(Ⅵ), while FEN showed the least toxicity. Two mixtures of CPF+CLO and Cr(Ⅵ)+CPF+CLO+ACE exhibited synergistic effects on the earthworms. The other two quaternary mixtures of CLO+FEN+ACE+Cr(Ⅵ) and Cr(Ⅵ)+FEN+CPF+ACE at low concentrations also displayed synergistic effects on the earthworms. In contrast, the mixture of Cr(Ⅵ)+FEN had the strongest antagonistic effects on E. fetida. Besides, the quinquenary mixture of Cr(Ⅵ)+FEN+CPF+CLO+ACE also exerted antagonistic effects. These findings highlighted the importance to evaluate chemical mixtures. Moreover, our data strongly pointed out that the avoidance tests could be used to assess the effects of combined effects.