Earthworm Tissues Research Articles

Ecotoxicology of mercury in tropical forest soils: Impact on earthworms

Mercury (Hg) is one of the most toxic nonessential trace metals in the environment, with high persistence and bioaccumulation potential, and hence of serious concern to environmental quality and public health. Emitted to the atmosphere, this element can travel long distances, far from emission sources. Hg speciation can lead to Hg contamination of different ecosystem components, as well as biomagnification in trophic food webs. To evaluate the effects of atmospheric Hg deposition in tropical forests, we investigated Hg concentrations in earthworm tissues and soils of two Forest Conservation Units in State of Rio de Janeiro, Brazil. Next, we performed a laboratory study of the biological responses (cast analysis and behavioral, acute, chronic and bioaccumulation ecotoxicological tests) of two earthworms species (Pontoscolex corethrurus and Eisenia andrei) to Hg contamination in tropical artificial soil (TAS) and two natural forest soils (NS) spiked with increasing concentration of HgCl2. Field results showed Hg concentrations up to 13 times higher in earthworm tissues than in forest soils, while in the laboratory Hg accumulation after 91-days of exposure was 25 times greater in spiked-soils with 128mgHgkg−1 (dry wt) than in control (unspiked) soils. In all the toxicity tests P. corethrurus showed a higher adaptability or resistance to mercury than E. andrei. The role of earthworms as environmental bioremediators was confirmed in this study, showing their ability to greatly bioaccumulate trace metals while reducing Hg availability in feces.

Investigating the Toxicity of Cu, CuO and ZnO Nanoparticles on Earthworms in Urban Soils

Even though some studies have shown that copper (Cu), copper oxide (CuO) and zinc oxide (ZnO) nanoparticles (NPs) are toxic to a number of organisms, fewer studies have investigated toxicity of these NPs in actual soils. This study investigated the effect of Cu, CuO and ZnO NPs in both urban and artificial soils. The aim was to examine the differences on these NPs’ ability to cause oxidative stress to organisms in urban and artificial soils. Earthworms, Eisenia fetida, (2 months old) were exposed to varying concentrations of NPs and bulk materials (used for comparison purposes) of Cu, CuO and ZnO ranging from 100-500 mg/kg, 100-4000 mg/kg and 100-4000 mg/kg, respectively, for 14 days, for each soil type. Superoxide dismutase (SOD), reduced glutathione (GSH) and hydrogen peroxide (H2O2) were measured at the end of exposure period. The accumulation of Cu and Zn in the earthworm tissues was measured using AAS. In urban soils, SOD, GSH and H2O2 all showed an initial increase as the concentration of NPs increased and but decreased at higher concentrations. Similar results for bulk materials were observed, though with less intensity. Cu and Zn accumulation in earthworm tissues increased as a function of NPs/bulk materials concentrations in both soils. Interestingly however, SOD, GSH and H2O2 from artificial soils for both NPs and bulk materials did not show significant differences from the controls, except at higher NPs/bulk materials concentrations.

Aldehyde dehydrogenase expression in Metaphire posthuma as a bioindicator to monitor heavy metal pollution in soil.

BackgroundSoil contamination and associated pollution plays a detrimental role in soil flora and fauna. Soil is processed and remodeled by subterranean earthworms, accordingly are referred to as soil chemical engineers. These worms, besides processing carbon and nitrogen, serve as minors for processing metals. In heavy metal contaminated soils, they accumulate heavy metals, which in turn cause altered gene expression, including aldehyde dehydrogenase (ALDH) enzymes. This study explores the possibility of ALDH expression in earthworms as a novel biomarker for the heavy metal contamination of soil.ResultsEarthworms cultured in contaminated soils accumulated significantly higher levels of Pb and Cd. Similarly, significantly higher levels of ALDH enzyme activities were observed in earthworms cultured in soils contaminated with Pb and Cd. The ALDH activity was found to be highest in worms cultured in 5 ppm heavy metal contaminated soils. Although, ALDH activities decreased as the heavy metal concentration in soil increased, they were significantly higher when compared to control worms cultured in uncontaminated soils. The accumulation of heavy metal in earthworms measured after 28 days decreased as the heavy metal concentration in soil increased.ConclusionsLevels of ALDH expression correlated with total Pb and Cd concentration in the earthworm tissue. This study showed that the ALDH activity in earthworms could potentially be used as a biomarker to show heavy metal pollution in soil.

Effect of cobalt and silver nanoparticles and ions on Lumbricus rubellus health and on microbial community of earthworm faeces and soil

The aim of this study was to investigate the impact of silver and cobalt, supplied both as ions and nanoparticles (Ag+, Co2+, AgNPs, CoNPs) through contaminated food to earthworms (Lumbricus rubellus), on their health as well as on microbial community of both soil and earthworm faeces. Earthworms and microbes were exposed to the contaminants in laboratory microcosms with artificial soil. Contaminants were supplied once a week for 5 weeks by spiking them on horse manure. The accumulation of CoNPs and Co2+ in earthworm tissues was two and three times greater than AgNPs and Ag+, respectively. Except for AgNPs, contaminants significantly affected microbial community structure of earthworm faeces by increasing G- bacteria, thus also increasing the bacteria/fungi ratio while decreasing the G+/G- bacteria ratio. Such shift was also reflected on soil microbial community, thus suggesting a close relationship between microbial community of soil and of earthworm faeces. Neither of the Co treatments affected soil microbial basal respiration whereas they increased the microbial biomass specific respiration or metabolic quotient, suggesting some stress induction on soil microorganisms. Earthworm health was strongly affected as revealed by the reduced fluidity of fatty acids extracted from the body tissues. In addition, the histological investigations, after the depuration period, showed positive results about the NPs toxicity. In particular, TUNEL-positive nuclei in epidermis and in peritoneum, suggest the presence of toxicosis.The ESEM-EDS technique revealed the presence of Ca-P spherules (calcification) between mouth and clitellum of earthworms fed with Co2+ contaminated food.

Impact of ionophore monensin on performance and Cu uptake in earthworm Eisenia andrei exposed to copper-contaminated soil

Exposure of beneficial soil organisms to chemical mixtures is of great concern and can result in unexpected deleterious consequences. We investigated the effects of concurrent soil contamination with monensin, a veterinary pharmaceutical and feed additive, and copper, on earthworm copper uptake and reproductive success. The animals were exposed for 14 or 28 days to both substances and the results showed that the Cu body burden of earthworms increases in the presence of monensin. The harmful effects of Cu on earthworm cocoon production were considerably higher when monensin was also present in the soil. To localise the copper in earthworm tissues, histological staining was performed using two different dyes (rubeanic acid and 5-4-(p-dimethylaminobenzylidene)-rhodanine). Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to quantify the Cu levels in the tissues. Cu was found predominantly in the gut wall. The Cu content in the body wall was at least ten times lower compared to the gut, but was proportional to the level of soil contamination. Concurrent soil contamination with monensin and copper resulted in higher earthworm Cu levels and in decreased reproductive success of these important soil decomposers.

Chemical and biological methods to evaluate the availability of heavy metals in soils of the Siena urban area (Italy)

A biogeochemistry field study was conducted in the Siena urban area (Italy) with the main objective of establishing the relationship between available amounts of heavy metals in soil assessed by a chemical method (soil fractionation) and bioavailability assessed by a biological method (bioaccumulation in earthworm tissues). The total content of traffic-related (Cd, Cu, Pb, Sb, Zn) and geogenic (Co, Cr, Ni, U) heavy metals in uncontaminated and contaminated soils and their concentrations in soil fractions and earthworms were used for this purpose. The bioavailability of heavy metals assessed by earthworms did not always match the availability defined by soil fractionation. Earthworms were a good indicator to assess the bioavailability of Pb and Sb in soil, while due to physiological mechanisms of regulation and excretion, Cd, Cu and Zn tissue levels in these invertebrates gave misleading estimates of their bioavailable pool. No relationship was identified between chemical and biological availability for the geogenic heavy metals, characterized by a narrow range of total contents in soil. The study highlighted that chemical and biological methods should be combined to provide more complete information about heavy element bioavailability in soils.

Glutathione-S-Transferase Production in Earthworm as Tool for Assessment of Heavy Metal Pollution in Abattoir Soil

The use of direct response of animals to environmental challenges by production of biomarkers is a better tool to assess environmental pollution than the conventional methods. This study aimed to measure Glutathione-S-transferase (GST) in earthworms as tools for assessing heavy metal pollution in abattoir soil. Five (5) replicates each of earthworm species (Libyodrilus violaceous, Eudrilus eugeniae and Alma millsoni), soil and rumen waste samples were collected from three (3) abattoir sites (Lafenwa, Gbonogun and Madojutimi abattoirs), and a control site located within Federal University of Agriculture Abeokuta, beside an undisturbed stream with no rumen waste. Heavy metal (Cu, Zn, Pb, Cd, Co, Cr, Ni and Mn) concentrations in rumen waste, abattoir soils and earthworm tissues were determined using Atomic Absorption Spectrophotometer. The pH and organic matter (OM) concentrations of the rumen waste and abattoir soils were determined by standard methods. GST activities in the earthworm tissues were determined through the conjugation of 1 mM reduced glutathione (GSH) with 1 mM 1-chloro-2,4-dinitrobenzene (CDNB). The rumen waste recorded significantly higher (p ≤ 0.05) % OM, heavy metal concentrations and pH level than in their respective abattoir soils. The mean heavy metal concentrations of Cu, Zn, Pb, Cd and Mn were highest in the tissue of earthworm species obtained from Lafenwa abattoir. A significantly (p ≤ 0.05) higher GST activities were recorded in the tissue of earthworm species obtained from Lafenwa and Gbonogun abattoirs. Libyodrilous violaceus obtained from Lafenwa abattoir recorded the highest GST activity (8.47±1.39) in their tissue followed by the ones from Gbonogun abattoir (8.21±0.85). A significant (p ≤ 0.05) positive correlations was observed between GST activities in earthworm tissues and heavy metal concentrations. GST activities can therefore be used to assess the level of heavy metal pollution in abattoir soils.

Earthworm metallothionein production as biomarker of heavy metal pollution in abattoir soil

The direct response of animals to environmental challenges, such as the production of biomarkers, is a better tool to assess environmental pollution than the conventional methods. In this study, the production of metallothionein (MT) in earthworms (Libyodrilus violaceous, Eudrilus eugeniae and Alma millsoni) was measured as tool for assessing heavy metal pollution in abattoir soil. Earthworm and abattoir soil samples were collected from three abattoir sites (Lafenwa, Gbonogun and Madojutimi) and a control site located beside an undisturbed stream located in Abeokuta, Ogun State, in South-western Nigeria. Heavy metal (Cu, Zn, Pb, Cd, Co, Cr, Ni and Mn) and MT concentrations were measured in the earthworm tissue and abattoir soil using standard methods. The concentrations of Cu, Zn, Pb, Cd and Mn were highest in the tissue of earthworms obtained from Lafenwa abattoir. The Bioaccumulation Factors (BAFs) for all the metals tested for were less than unity, except for Cd which had a BAF>1. The MT concentrations recorded in the earthworm samples from the Gbonogun and Lafenwa abattoir sites were significantly higher (p≤0.05) than in earthworms from Madojutimi. The lowest MT concentration was recorded in earthworms from the control. Significant (p≤0.05) positive correlations were observed between MT and heavy metal concentrations in all earthworm species indicating that MT concentrations can be used as biomarker of heavy metal pollution in abattoir soils.

Comparative toxicity and bioaccumulation of fenvalerate and esfenvalerate to earthworm Eisenia fetida

More attention is being paid to the enantioselective toxicity of chiral pesticides. However, limited investigations have been done to assess the ecological risks of chiral pesticides to soil community. Fenvalerate (FV), an extensively used synthetic pyrethroid, is a typical chiral pesticide. The most insecticidally active enantiomer of FV, esfenvalerate (ESFV), also has been marketed and widely used. In this study, the toxicological sensitivity and bioaccumulation of FV and ESFV in earthworms were assessed. The results showed that FV was less toxic than ESFV, but more accumulated in earthworms. ESFV was at least 4 times more toxic to earthworms than FV according to the filter paper contact toxicity test and the artificial soil test. Enantiospecific induction in oxidative stress was observed in earthworms exposed to FV and ESFV. The bioaccumulation of FV and ESFV in earthworm tissues was also enantioselective, preferentially accumulating FV. The uptake of ESFV by earthworms was lower than that of FV, so that the biota to soil accumulation factor (BSAF) value of ESFV was lower than that of FV. Our findings suggest that the enantioselective toxicity and bioaccumulation of chiral pesticides should be considered for evaluating ecological risks of these compounds to non-target organisms.

Accumulation of heavy metals during vermicomposting by earthwormEisenia fetida

Earthworms form one of the major macrofauna among soil biota to maintain dynamic equilibrium and regulate soil fertility. Their existence depends on adequate moisture, soil texture, pH, electrolyte concentration and food source in the given ecosystem. The present study focusses primarily on the potential of Eisenia fetida Savigny to accumulate heavy metals from contaminated soil during vermicomposting. Samples of contaminated soil were collected from five different sites in the vicinity of Buddha Nullah at Ludhiana, and upon analysis Lead, Chromium and Nickel were recorded as the prominent metals of the area. The potential of bioaccumulation was tested by adding metals to artificial soil in ratios similar to those found at sites and earthworms were released into the trays. The results indicated that bioaccumulation of heavy metals (Pb, Cr, Ni) takes place in earthworm tissue. The percent remediation in soil with highest dose of lead was 5.54%, 4.53% for chromium and 48% for nickel indicated that as compared to other metals nickel was remediated easily.

Accumulation, biotransformation, and multi-biomarker responses after exposure to arsenic species in the earthworm Eisenia fetida.

Earthworms (Eisenia fetida) were exposed to OECD soils contaminated with arsenite (29.3 mg kg-1), arsenate (35.2 mg kg-1), monomethylarsonate (342.5 mg kg-1) and dimethylarsinate (373.0 mg kg-1) for 64 days. The exposure concentration for the four arsenic species was set at one-tenth of 14 d-LC50 in order to compare their toxicity. Eight biomarkers including superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, glutathione reductase, reduced glutathione, lipid peroxidation and metallothioneins were analyzed in the organisms. A multi-biomarker approach, the integrated biomarker response (IBR) index, was adopted to summarize the multi-biomarker responses to a single value, reflecting the integrated stress of different arsenic species on earthworms. Furthermore, total arsenic and arsenic speciation were analyzed in earthworm tissue to evaluate the relationship between arsenic accumulation and biomarker responses at the molecular and subcellular levels and to observe the role of arsenic biotransformation in earthworms. The results showed that the toxicity of the four arsenic species was ranked as: arsenite > arsenate > monomethylarsonate and dimethylarsinate. Although organic arsenics showed a low degree of biotoxicity, they could be turned into highly toxic inorganic arsenics under the effect of demethylation, which caused a toxic effect on organisms. The biomarker responses indicated that a sub-lethal dose of both arsenite and arsenate could trigger the response of the antioxidant defense system and cause oxidative damage when the protective capacity of the system was exhausted. Arsenic in earthworms could be detoxified during the process of biotransformation, where inorganic arsenics were converted into organic arsenics, which would then be excreted out. Based on these results, it was proved that different arsenic species showed different degrees of toxicity. Therefore, arsenic species should be differentiated in order to obtain accurate results in quality/risk assessment programs.

Earthworms Eisenia fetida affect the uptake of heavy metals by plants Vicia faba and Zea mays in metal-contaminated soils

Earthworms increase the availability of heavy metals in some situations and aid in maintaining the structure and quality of soil. The introduction of earthworms into metal-contaminated soils has been suggested as an aid for phytoremediation processes. In Wallonia, Belgium, a century of industrial metallurgic activities has led to the substantial pollution of soils by heavy metals, including copper (Cu), zinc (Zn), lead (Pb) and cadmium (Cd), due to atmospheric dusts. Two plant species, Vicia faba and Zea mays, and earthworms (Eisenia fetida) (Savigny, 1826) were exposed to different concentrations of long-term-contaminated soils for 42 days. The soil samples, which were collected from the land surrounding a former Zn-Pb ore-treatment plant, exhibited different levels of heavy metals. Our aim was to evaluate the role of earthworms E. fetida on the availability of metals in soils and their effects on metal uptake by V. faba and Z. mays plants at different soil concentrations.The results suggest that earthworms and plants modified the availability of metals in contaminated soils after 42 days of exposure. Earthworm life-cycle parameters were affected by metal contamination and/or the addition of plants; cocoon production and weight were more responsive to adverse conditions than earthworm survival or weight change. The concentrations of Pb and Cd in earthworm tissues decreased in the presence of plants. Results showed that metal accumulation in plants depended on the metal element considered and the presence of earthworms. However, the presence of earthworms did not change the concentrations of metals in plants, except for Cd. In the presence or absence of earthworms, V. faba accumulated higher concentrations of Cu and Zn compared with Z. mays, which accumulated higher concentrations of Cd. These findings have revealed that earthworm activities can modify the availability of heavy metals for uptake by plants in contaminated soils. Moreover, the study results show that the ecological context of phytoremediation should be broadened by considering earthworm-plant-soil interaction, which influence both the health of the plant and the uptake of heavy metals by plants.

Earthworm Uptake Routes and Rates of Ionic Zn and ZnO Nanoparticles at Realistic Concentrations, Traced Using Stable Isotope Labeling.

The environmental behavior of ZnO nanoparticles (NPs), their availability to, uptake pathways by, and biokinetics in the earthworm Lumbricus rubellus were investigated using stable isotope labeling. Zinc isotopically enriched to 99.5% in (68)Zn ((68)Zn-E) was used to prepare (68)ZnO NPs and a dissolved phase of (68)Zn for comparison. These materials enabled tracing of environmentally relevant (below background) NP additions to soil of only 5 mg (68)Zn-E kg(-1). Uptake routes were isolated by introducing earthworms with sealed and unsealed mouthparts into test soils for up to 72 h. The Zn isotope compositions of the soils, pore waters and earthworms were then determined using multiple collector inductively coupled plasma mass spectrometry. Detection and quantification of (68)Zn-E in earthworm tissue was possible after only 4 h of dermal exposure, when the uptake of (68)Zn-E had increased the total Zn tissue concentration by 0.03‰. The results demonstrate that at these realistic exposure concentrations there is no distinguishable difference between the uptake of the two forms of Zn by the earthworm L. rubellus, with the dietary pathway accounting for ∼95% of total uptake. This stands in contrast to comparable studies where high dosing levels were used and dermal uptake is dominant.

Assimilation of labile carbon and particulate organic matter by tropical endogeic earthworms Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta)

Endogeic earthworms often dominate in biomass in the soil macrofauna of temperate and tropical zones. Representatives of this morphoecological group play a unique role in ecosystems due to their ability to utilize stabilized organic matter from mineral soil horizons, but the mechanisms underlying this ability are still poorly understood. Endogeic earthworms Pontoscolex corethrurus reach a remarkably high density in the alluvial sandy soil of a gallery forest along the Dong Nai River in the Cat Tien National Park, southern Vietnam. This soil is extremely poor in organic matter, and the earthworms appear to depend on labile carbon from plant roots and detritus. In a 28-day laboratory experiment, food availability to P. corethrurus has been manipulated by supplementing the soil either with different size fractions of plant detritus or with labile organic carbon (glucose), both enriched in 13C in order to monitor carbon assimilation in earthworm tissues. The results have shown that P. corethrurus earthworms fail to utilize carbon from plant debris but effectively assimilate glucose carbon even when it is added at a very low concentration. Thus, the high abundance of these earthworms in poor sandy soils is apparently explained by their ability to assimilate root-derived labile carbon. Moreover, the presence of carbon available to soil microorganisms allows the earthworms to utilize native soil organic carbon and nitrogen.

Bioremediation of heavy metals and petroleum hydrocarbons in diesel contaminated soil with the earthworm: Eudrilus eugeniae.

A laboratory study on the bioremediation of diesel contaminated soil with the earthworm Eudrilus eugeniae (Kingberg) was conducted. 5 ml of diesel was contaminated into soils in replicates and inoculated with E. eugeniae for 90 days. Physicochemical parameters, heavy metals and total petroleum hydrocarbons were analyzed using AAS. BTEX in contaminated soil and tissues of earthworms were determined with GC-FID. The activities of earthworms resulted in a decrease in pH (3.0 %), electrical conductivity (60.66 %), total nitrogen (47.37 %), chloride (60.66 %), total organic carbon (49.22 %), sulphate (60.59 %), nitrate (60.65 %), phosphate (60.80 %), sodium (60.65 %), potassium (60.67 %), calcium (60.67 %), magnesium (60.68 %), zinc (60.59 %), manganese (60.72 %), copper (60.68 %), nickel (60.58 %), cadmium (60.44 %), vanadium (61.19 %), chromium (53.60 %), lead (60.38 %), mercury (61.11 %), arsenic (80.85 %), TPH (84.99 %). Among the BTEX constituents, only benzene (8.35 %) was detected in soil at the end of the study. Earthworm tissue analysis showed varying levels of TPH (57.35 %), benzene (38.91 %), toluene (27.76 %), ethylbenzene (42.16 %) and xylene (09.62 %) in E. eugeniae at the end of the study. The study has shown that E. eugeniae could be applied as a possible bioremediator in diesel polluted soil.

Thresholds of arsenic toxicity to Eisenia fetida in field-collected agricultural soils exposed to copper mining activities in Chile

Several previous studies highlighted the importance of using field-collected soils—and not artificially-contaminated soils—for ecotoxicity tests. However, the use of field-collected soils presents several difficulties for interpretation of results, due to the presence of various contaminants and unavoidable differences in the physicochemical properties of the tested soils. The objective of this study was to estimate thresholds of metal toxicity in topsoils of 24 agricultural areas historically contaminated by mining activities in Chile. We performed standardized earthworm reproduction tests (OECD 222 and ISO 11268-2) with Eisenia fetida. Total soil concentrations of Cu, As, Zn, and Pb were in the ranges of 82–1295mgkg−1, 7–41mgkg−1, 86–345mgkg−1, and 25–97mgkg−1, respectively. In order to differentiate between the effects of different metals, we used regression analysis between soil metal concentrations and earthworm responses, as well as between metal concentrations in earthworm tissues and earthworm responses. Based on regression analysis, we concluded that As was a metal of prime concern for Eisenia fetida in soils affected by Cu mining activities, while Cu exhibited a secondary effect. In contrast, the effects of Zn and Pb were not significant. Soil electrical conductivity was another significant contributor to reproduction toxicity in the studied soils, forcing its integration in the interpretation of the results. By using soils with electrical conductivity ≤0.29dSm−1 (which corresponds to EC50 of salt toxicity to Eisenia fetida), it was possible to isolate the effect of soil salinity on earthworm reproduction. Despite the confounding effects of Cu, it was possible to determine EC10, EC25 and EC50 values for total soil As at 8mgkg−1, 14mgkg−1 and 22mgkg−1, respectively, for the response of the cocoon production. However, it was not possible to determine these threshold values for juvenile production. Likewise, we were able to determine EC10, EC25 and EC50 of earthworm tissue As of 38mgkg−1, 47mgkg−1, and 57mgkg−1, respectively, for the response of the cocoon production. Finally, we determined the no-observed effect concentration of tissue As in E. fetida of 24mgkg−1. Thus, earthworm reproduction test is applicable for assessment of metal toxicity in field-collected soils with low electrical conductivity, while it might have a limited applicability in soils with high electrical conductivity because the salinity-induced toxicity will hinder the interpretation of the results.

Uptake routes and toxicokinetics of silver nanoparticles and silver ions in the earthworm Lumbricus rubellus.

Current bioavailability models, such as the free ion activity model and biotic ligand model, explicitly consider that metal exposure will be mainly to the dissolved metal in ionic form. With the rise of nanotechnology products and the increasing release of metal-based nanoparticles (NPs) to the environment, such models may increasingly be applied to support risk assessment. It is not immediately clear, however, whether the assumption of metal ion exposure will be relevant for NPs. Using an established approach of oral gluing, a toxicokinetics study was conducted to investigate the routes of silver nanoparticles (AgNPs) and Ag(+) ion uptake in the soil-dwelling earthworm Lumbricus rubellus. The results indicated that a significant part of the Ag uptake in the earthworms is through oral/gut uptake for both Ag(+) ions and NPs. Thus, sealing the mouth reduced Ag uptake by between 40% and 75%. An X-ray analysis of the internal distribution of Ag in transverse sections confirmed the presence of increased Ag concentrations in exposed earthworm tissues. For the AgNPs but not the Ag(+) ions, high concentrations were associated with the gut wall, liver-like chloragogenous tissue, and nephridia, which suggest a pathway for AgNP uptake, detoxification, and excretion via these organs. Overall, the results indicate that Ag in the ionic and NP forms is assimilated and internally distributed in earthworms and that this uptake occurs predominantly via the gut epithelium and less so via the body wall. The importance of oral exposure questions the application of current metal bioavailability models, which implicitly consider that the dominant route of exposure is via the soil solution, for bioavailability assessment and modeling of metal-based NPs.

Bioavailability and release of nonextractable (bound) residues of chiral cycloxaprid using geophagous earthworm Metaphire guillelmi in rice paddy soil

The widespread adoption of neonicotinoids has led to a move away from integrated pest management (IPM) and caused adverse effects on non-target invertebrate species. Due to their living in close contact with and consuming large amounts of soil, earthworms are a model organism used to study bioaccumulation. We investigated the bioaccumulation and release of bound, or non-extractable, residues (BRs) of 14C labeled racemic cycloxaprid (CYC) and its individual enantiomers by the geophagous earthworm Metaphire guillelmi. In a previous work, the fraction of BRs of 14C-CYC individual enantiomers reached up to 70–85% of the initially spiked radioactivity after 100d of treatment. The bulk volume of the soil was then diluted by a factor of 15 with fresh soil. Here we showed that after earthworms lived in the soil-bound residues for 28d, 11–25% of the previously bound radioactivity in soil was extractable by solvent, mineralized to CO2, and accumulated in earthworm tissues. While earthworms were exposed to 14C-CYC a two-compartment accumulation model could explain the bio-accumulation as individual enantiomers. At the end of the experiment, the biota-sediment accumulation factors were between 0.59 and 0.82, which suggested CYC immobilization in the soil resulted in its bioavailability being reduced which enhanced its degradation. Additionally, the elimination of CYC individual enantiomers from M. guillelmi was fitted to an availability-adjusted decay model with a half-life of 9d. Stereoselective release or bioavailability between CYC enantiomers was not observed. These results provide the important data about the release of BRs of CYC and potential transfer in the food chain to support the long-term environmental risk assessment of neonicotinoids.

Short-term soil bioassays may not reveal the full toxicity potential for nanomaterials; bioavailability and toxicity of silver ions (AgNO3) and silver nanoparticles to earthworm Eisenia fetida in long-term aged soils

This study investigated if standard risk assessment hazard tests are long enough to adequately provide the worst case exposure for nanomaterials. This study therefore determined the comparative effects of the aging on the bioavailability and toxicity to earthworms of soils dosed with silver ions and silver nanoparticles (Ag NP) for 1, 9, 30 & 52 weeks, and related this to the total Ag in the soil, Ag in soil pore water and earthworm tissue Ag concentrations. For ionic Ag, a classical pattern of reduced bioavailability and toxicity with time aged in the soil was observed. For the Ag NP, toxicity increased with time apparently driven by Ag ion dissolution from the added Ag NPs. Internal Ag in the earthworms did not always explain toxicity and suggested the presence of an internalised, low-toxicity Ag fraction (as intact or transformed NPs) after shorter aging times. Our results indicate that short-term exposures, without long-term soil aging, are not able to properly assess the environmental risk of Ag NPs and that ultimately, with aging time, Ag ion and Ag NP effect will merge to a common value.

Antioxidant and behavior responses of earthworms after introduction to a simulated vermifilter environment

Vermifiltration is a new technology for treating wastewater with a high organic loading, but there is almost no published information on the biochemical and behavioral response of earthworms in a vermifilter environment. This study measured antioxidase enzyme (AOE) activities and reactive oxygen species (ROS) and malondialdehyde (MDA) levels in tissues of earthworms for a period of 56 d after transfer into simulated vermifilters. Three vermifilter media were tested. In general AOE activities, ROS and MDA were elevated for the first 3–5 d after transfer, variable for approximately the next 7 d, and statistically indistinguishable from controls after 15 d. Similarly, earthworm activity as measured by daily burrowing length was initially enhanced but converged with that of controls after 6 d. Removal of chemical oxygen demand (COD) from artificial wastewater was significantly correlated with AOE and ROS in earthworm tissues, and daily burrowing length of earthworms, but none of these parameters was correlated to NH4+-N removal rate, suggesting earthworms do not play a direct role in nitrogen removal in vermifilters. The data provide useful information for vermifilter operators about the biochemical adaptive process earthworms undergo when introduced to a vermifilter environment and the lag time between set up and reliable operation of a vermifilter. The results could potentially lead to development of preconditioning treatments to shorten the settling-down time for newly set up vermifilters. Maximum burrow depth was reduced in simulated vermifilters, suggesting an optimal depth for vermifilter substrates. The three vermifilter media tested differed in performance and possible reasons are briefly discussed.