Dietary uptake of superlipophilic compounds by earthworms (Eisenia andrei)

A User-Friendly Kinetic Model Incorporating Regression Models for Estimating Pesticide Accumulation in Diverse Earthworm Species Across Varied Soils

Existing models for estimating pesticide bioconcentration in earthworms exhibit limited applicability across different chemicals, soils and species which restricts their potential as an alternative, intermediate tier for risk assessment. We used experimental data from uptake and elimination studies using three earthworm species (Lumbricus terrestris, Aporrectodea caliginosa, Eisenia fetida), five pesticides (log Kow 1.69-6.63) and five soils (organic matter content = 0.972-39.9 wt %) to produce a first-order kinetic accumulation model. Model applicability was evaluated against a data set of 402 internal earthworm concentrations reported from the literature including chemical and soil properties outside the data range used to produce the model. Our models accurately predict body load using either porewater or bulk soil concentrations, with at least 93.5 and 84.3% of body load predictions within a factor of 10 and 5 of corresponding observed values, respectively. This suggests that there is no need to distinguish between porewater and soil exposure routes or to consider different uptake and elimination pathways when predicting earthworm bioconcentration. Our new model not only outperformed existing models in characterizing earthworm exposure to pesticides in soil, but it could also be integrated with models that account for earthworm movement and fluctuating soil pesticide concentrations due to degradation and transport.

Effect of polycyclic aromatic compounds (PAH & Polar-PAC) availability on their ecotoxicity towards terrestrial organisms

The exposure of terrestrial organisms to soils freshly contaminated by polycyclic aromatic compounds (PACs, including PAHs and polar-PACs) is known to cause significant toxicity effects. However, historically contaminated soils, such as former coking plant soils, usually induce a limited toxic impact, due to the "aging" phenomenon which is the result of several processes causing a reduction of PAC availability over time. For a better understanding of these behaviors, this study aimed to compare the toxic responses of terrestrial organisms exposed to aged contaminated soils and their counterparts submitted to a moderate heating process applied to increase PAC availability. Two aged "raw" soils (limited PAC availability) were selected for their representativeness of former industrial soils in terms of PAC contamination. These soils were submitted either to moderate heating (expected PAC availability increase) or solvent-extraction (expected PAC removal). Physico-chemical parameters, contamination levels and availability were determined for these three soil modalities. Additionally, standardized limit bioassays on plants and earthworms were performed to assess soil ecotoxicity. The findings demonstrated that historically contaminated soils exposed to moderate heating induced the highest ecotoxic responses from terrestrial organisms. Heating increased PAC (bio)availability, without modifying any other soil physico-chemical properties. These results pointed out the importance of considering the contamination availability parameter in risk evaluation and also provide a possible tool for protective long-term risk assessment.

Fate and bioavailability of four conazole fungicides in twelve different arable soils - Effects of soil and pesticide properties

The objective of this study is to characterize changes in the fate, behaviour and bioavailability of four conazole fungicides - CFs (prochloraz - PRO, tebuconazole - TEB, epoxiconazole - EPO, flusilazole - FLU) in 12 diverse agricultural soils in complex microcosm systems consisting of agriculturally-used fluvisols, plants (Lactuca sativa), earthworms (Eisenia fetida) and passive samplers (SPME, Empore™ discs, silicone rubber). Due to great variability of the data and other methodological problems, the in-matrix passive samplers failed to be indicators of pore-water concentration and (bio)availability/(bio)accessibility of CFs. A dissipation of all CFs followed the first order kinetics (usually after initial lag phase) with large span of resulting half-lives (7-670 d) depending on soils and compounds. In many soils, the model revealed the ending plateau, which indicates the non-degradable or slowly-degradable residues. The half-lives and the residues were generally higher for EPO and FLU, than for PRO and TEB. Greater but slower total dissipation of CFs was observed in soils with higher percentage of organic matter. Earthworm concentrations were highest at first sampling time (14 days) and considerably decreased afterwards often resulting in PRO concentration below LOQ. Earthworm uptake was influenced by amount of organic matter and soil texture. Accumulation to lettuce roots was generally higher than to leaves and differed greatly among CFs. Concentration shoot to root ratios were generally the lowest for FLU (0.04) and highest for TEB (0.37). PRO was not detected in lettuce leaves during experiment. The study brings new results on fate and bioavailability of CFs in soils.

Uptake kinetics of pesticides chlorpyrifos and tebuconazole in the earthworm Eisenia andrei in two different soils

Agriculture is today indispensably connected with enormous use of pesticides. Despite tough regulation, their entrance into soil cannot be excluded and they might enter soil organisms and plants and continue further to terrestrial food chains. This study was conducted to investigate the bioaccumulation of two pesticides currently used in large amounts, the insecticide chlorpyrifos (CLP) and the fungicide tebuconazole (TBZ). Their detailed uptake kinetics in the model earthworm species Eisenia andrei were measured in two arable soils differing in organic carbon content (1.02 and 1.93% respectively). According to our results, a steady state was reached after 3-5 days for both pesticides and soils. The values of bioaccumulation factors calculated at the steady state ranged from 4.5 to 6.3 for CLP and 2.2-13.1 for TBZ. Bioaccumulation factors were also calculated as the ratio of uptake and elimination rate constants with results comparable with steady-state bioaccumulation factors. The results suggested that the degradation and bioaccumulation of tested compounds might be influenced by other factors than only total organic carbon (e.g. clay content). The lower K_oc and hydrophobicity of TBZ relative to CLP probably led to higher availability of TBZ through pore water exposure. On the other hand, CLP's higher hydrophobicity probably caused an increase in availability by its additional uptake via ingestion. To enable a proper ecological risk assessment of current pesticides in soils, it is necessary to accurately determine their bioaccumulation in soil invertebrates. We believe that our study not only brings such information for two specific pesticides but also addresses key methodological issues in this area.

Adsorption of phenanthrene by earthworms - A pathway for understanding the fate of hydrophobic organic contaminants in soil-earthworm systems

The fate of hydrophobic organic contaminants (HOCs) in soil-earthworm systems is an important foundation for soil pollution risk assessment and pollution control. Equilibrium partitioning is considered to be the main mechanism by which HOCs enter earthworms and, as such, a mechanistic model has been developed to estimate the earthworm-water partition coefficients (K_w-w). In the present study, the adsorption of phenanthrene (PHE) by earthworm tissue was investigated to evaluate the validity of the mechanistic models. Results revealed that K_w-w derived from the mechanistic model (346.90) was lower than that derived from the sorption experiments (410.76), indicating that apart from lipid fractions, other components in earthworms, such as protein fractions, might also play an important role in the adsorption of HOCs by earthworm. Besides, the difference between the mechanistic model for earthworm and partition-limited model used for plants are few, indicating that uptake and accumulation mechanisms of HOCs by earthworms and plants are highly consistent internally and are, essentially actually identical. It is also suggested that environmental fate of HOCs in soil-soil biota systems is dominated by their high hydrophobicity. Based on these conclusions, an improved mechanistic model for predicting the uptake of organic contaminants by earthworms has been proposed, which needs to be further evaluated. Furthermore, the feasibility of using vermiaccumulation in vermiremediation of soil contaminated by HOCs was discussed. The adsorption of PHE by earthworm sub-organism fractions (pre-clitellum, clitellum and post-clitellum) and tissue fractions (body wall and gut) were also investigated to interpret the distribution pattern of HOCs in earthworms. At the sub-organism level, the adsorption capacity of PHE by different regions of the earthworm followed the order: post-clitellum > clitellum > pre-clitellum, meaning the distribution of PHE along the earthworm contributes not only to their chemical composition but also to the life activity of earthworms such as circular system. At the tissue level, the gut showed greater affinity with PHE than that of the body wall indicating that the distribution of PHE is mainly due to chemical components at the tissue levels. These results might provide additional understanding of the fate of HOCs in soil-earthworm systems.

Review of existing terrestrial bioaccumulation models and terrestrial bioaccumulation modeling needs for organic chemicals

Protocols for terrestrial bioaccumulation assessments are far less-developed than for aquatic systems. This article reviews modeling approaches that can be used to assess the terrestrial bioaccumulation potential of commercial organic chemicals. Models exist for plant, invertebrate, mammal, and avian species and for entire terrestrial food webs, including some that consider spatial factors. Limitations and gaps in terrestrial bioaccumulation modeling include the lack of QSARs for biotransformation and dietary assimilation efficiencies for terrestrial species; the lack of models and QSARs for important terrestrial species such as insects, amphibians and reptiles; the lack of standardized testing protocols for plants with limited development of plant models; and the limited chemical domain of existing bioaccumulation models and QSARs (e.g., primarily applicable to nonionic organic chemicals). There is an urgent need for high-quality field data sets for validating models and assessing their performance. There is a need to improve coordination among laboratory, field, and modeling efforts on bioaccumulative substances in order to improve the state of the science for challenging substances.

Influence of bioaugmentation on biodegradation of phenanthrene-contaminated soil by earthworm in lab scale

BACKGROUND

Use of earthworm to eliminate the phenanthrene from the soil (bioaccumulation) is developed as an economical method. Bioaugmentation of microorganism was used for promotion of bioaccumulation by earthworm. The aim of this study was to determine the bioaccumulation or biodegradation of phenanthrene by Eisenia fetida and bacterial consortium in polluted soil.

METHODS

The amount of 0.4 kg of the polluted soil in the ratio of 10 and 30 mg phenanthrene per kg of dry soil was transferred into each pot. Afterwards, bacteria and earthworms were added to each pot in separate and combination. The samples were kept under field conditions, and the retention concentrations of phenanthrene were analyzed after 8 weeks.

RESULTS

Results showed that the Eisenia fetida was able to significantly remove phenanthrene from the polluted soil samples. Bioaccumulation and bioaugmentation alone have the removal efficiency of 60.24% and 50.3%, respectively. In the combined mode, phenanthrene removal efficiency was 63.81%.

CONCLUSIONS

The current study indicated that the use of earthworms, could improve both phenanthrene bioavailability and microbial activity, which led to enhancing removal of carbon-based pollutants.

Bioaccumulation of fullerene (C60) and corresponding catalase elevation in Lumbriculus variegatus

Fullerene (C(60)), with its unique physical properties and nanometer size, has been mass-produced for many applications in recent decades. The increased likelihood of direct release into the environment has raised interest in understanding both the environmental fate and corresponding biological effects of fullerenes to living organisms. Because few studies have emphasized fullerene uptake and resulting biochemical responses by living organisms, a toxicity screening test and a 28-d bioaccumulation test for Lumbriculus variegatus were performed. No mortality was observed in the range of 0.05 mg C(60) /kg dry sediment to 11.33 mg C(60) /kg dry sediment. A biota-sediment accumulation factor of micron-sized fullerene agglomerates (µ-C(60)) was 0.032 ± 0.008 at day 28, which is relatively low compared with pyrene (1.62 ± 0.22). Catalase (CAT) activity, an oxidative stress indicator, was elevated significantly on day 14 for L. variegatus exposed to µ-C(60) (p = 0.034). This peak CAT activity corresponded to the highest body residues observed in the present study, 199 ± 80 µg C(60) /kg dry weight sediment. Additionally, smaller C(60) agglomerate size increased bioaccumulation potential in L. variegatus. The relationship between C(60) body residue and the increased CAT activity followed a linear regression. All results suggest that C(60) has a lower bioaccumulation potential than pyrene but a higher potential to induce oxidative stress in L. variegatus.

Uptake kinetics of five hydrophobic organic pollutants in the earthworm Eisenia fetida in six different soils

Hydrophobic organic contaminants in soils may pose toxicity or transfer to food chains after their uptake to soil biota. However, uptake data for earthworms are usually limited, as: (a) only fixed exposure times are studied instead of whole uptake kinetics and (b) studies including compounds with different environmental properties and more than two soils of different properties are quite rare. In our study, five persistent organic pollutants (phenanthrene, pyrene, lindane, p,p'-dichlorodiphenyltrichloroethane (p,p'-DDT), and polychlorinated biphenyl congener No. 153 (PCB 153)) were added to six soils of a wide range of soil properties. Detailed kinetics of uptake to earthworms Eisenia fetida were measured. Results indicated that an equilibrium of concentrations for p,p'-DDT and PCB 153 was reached after 11 days of exposure in all soils. Uptake of phenanthrene, pyrene, and lindane was strongly influenced by the decrease in concentrations in the soils, resulting in peak-shaped accumulation curves. Only in soils with the highest total organic carbon content (7.9 and 20.2%), the equilibrium of lindane concentrations was achieved (after 17 and 5 days of exposure, respectively). We recommend calculating bioaccumulation factors as a ratio of the uptake and elimination rate constants to precise the risk assessment.

Bioaccumulation of 14C60 by the earthworm Eisenia fetida

Carbon fullerenes, including buckminsterfullerene (C(60)), are increasingly available for numerous applications, thus increasing the likelihood of environmental release. This calls for information about their bioavailability and bioaccumulation potential. In this study, (14)C-labeled C(60) and (14)C-phenanthrene (positive control) were added separately to soils of varying composition and organic carbon content (OC), and their bioaccumulation in the earthworm Eisenia fetida was compared. Biota-sediment accumulation factors (BSAF) were measured after 24 h depuration in soils with high C(60) dosages (60, 100, and 300 mg-C(60) kg(-1) dry soil), which exceed the soil sorption capacity, as well as in soils with a low C(60) dose (0.25 mg kg(-1)) conducive to a high fraction of sorbed molecular C(60). The BSAF value for the low-dose soil (0.427) was 1 order of magnitude lower than for less hydrophobic phenanthrene (7.93), inconsistent with the equilibrium partition theory that suggests that BSAF should be constant and independent of the K(OW) value of the chemical. Apparently, the large molecular size of C(60) hinders uptake and bioaccumulation. Lower BSAF values (0.065-0.13) were measured for high-dose soils, indicating that C(60) bioaccumulates more readily when a higher fraction of molecular C(60) (rather than larger precipitates) is available. For the high-dose tests (heterogeneous C(60) system), soil OC content did not significantly affect the extent of C(60) bioaccumulation after 28 d of incubation, although higher OC content resulted in faster initial bioaccumulation. For low-dose soils, C(60) BSAF decreased with increasing soil OC, as commonly reported for hydrophobic chemicals due to partitioning into soil OC. There was no detectable transformation of (14)C(60) in either soil or worm tissue. Overall, the relatively low extent but rapid bioaccumulation of C(60) in E. fetida suggests the need for further studies on the potential for trophic transfer and biomagnification.

Accumulation of polybrominated diphenyl ethers, hexabromobenzene, and 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane in earthworm (Eisenia fetida). Effects of soil type and aging

In the present study the accumulation potentials in earthworms (Eisenia fetida) of selected brominated flame retardants (BFRs) were investigated. The tested BFRs, including polybrominated diphenyl ethers (PBDEs), hexabromobenzene (HBB), and 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane (TBECH), were found to be bioavailable to Eisenia fetida, and they accumulated in the earthworms. To our knowledge, this is the first published study to address the bioaccumulation potential of TBECH in terrestrial biota. Aging the soil resulted in decreased accumulation of TBECH, HBB, and PBDEs with six or less bromine atoms. However, no effect of soil aging was seen for BDEs 183 or 209, possibly due to their low mobility in soil. The use of different soils (artificial OECD soil and two natural Swedish soils) also affected the degree of accumulation in the worms. The results indicate that use of the generally accepted standard OECD soil may overestimate accumulation of organic contaminants by earthworms, due to high bioavailability of the contaminants and/or weight loss of the worms in it. Further, the accumulation of selected PBDEs and HBB was compared to the accumulation of their chlorinated analogues. Brominated compounds accumulated to the same or a lesser extent than their chlorinated counterparts.

Effect of temephos on cholinesterase activity in the earthworm Eisenia fetida (Oligochaeta, Lumbricidae)

In this study, adult Eisenia fetida earthworms were exposed to the sub-lethal concentrations of temephos using the contact filter paper test procedure. Since temephos is an organophosphate pesticide, its effects on earthworms were determined by measuring ChE inhibition--a known biomarker of exposure. The ChE activity was measured after a short time of exposure--1 and 2 h. As expected, the lowest ChE activity (72.70% and 38.03% inhibition) was measured at the highest concentration of temephos (120 ng cm(-2)) applied. More interestingly, at the 0.12 ng cm(-2) concentration the ChE activity increased up to 36.28% of activity in the control in all three conducted experiments. Dose-response curves showed an inverted U-shape characteristic for hormesis. This hormetic-like effect could be important for health status of an earthworm.

Ecotoxicity of a polycyclic aromatic hydrocarbon (PAH)-contaminated soil

Soil samples from a former cokery site polluted with polycyclic aromatic hydrocarbons (PAHs) were assessed for their toxicity to terrestrial and aquatic organisms and for their mutagenicity. The total concentration of the 16 PAHs listed as priority pollutants by the US Environmental Protection Agency (US-EPA) was 2634+/-241 mg/kgdw in soil samples. The toxicity of water-extractable pollutants from the contaminated soil samples was evaluated using acute (Vibrio fischeri; Microtox test, Daphnia magna) and chronic (Pseudokirchneriella subcapitata, Ceriodaphnia dubia) bioassays and the EC values were expressed as percentage water extract in the test media (v/v). Algal growth (EC50-3d=2.4+/-0.2% of the water extracts) and reproduction of C. dubia (EC50-7d=4.3+/-0.6%) were the most severely affected, compared to bacterial luminescence (EC50-30 min=12+/-3%) and daphnid viability (EC50-48 h=30+/-3%). The Ames and Mutatox tests indicated mutagenicity of water extracts, while no response was found with the umu test. The toxicity of the soil samples was assessed on the survival and reproduction of earthworms (Eisenia fetida) and collembolae (Folsomia candida), and on the germination and growth of higher plants (Lactuca sativa L.: lettuce and Brassica chinensis J.: Chinese cabbage). The EC50 values were expressed as percentage contaminated soil in ISO soil test medium (weight per weight-w/w) and indicated severe effects on reproduction of the collembola F. candida (EC50-28 d=5.7%) and the earthworm E. fetida (EC50-28 d=18% and EC50-56 d=8%, based on cocoon and juvenile production, respectively). Survival of collembolae was already affected at a low concentration of the contaminated soil (EC50-28 d=11%). The viability of juvenile earthworms was inhibited at much lower concentrations of the cokery soil (EC50-14 d=28%) than the viability of adults (EC50-14 d=74%). Only plant growth was inhibited (EC50-17d=26%) while germination was not. Chemical analyses of water extracts allowed us to identify inorganic water-extractable pollutants as responsible for toxicity on aquatic species, especially copper for effects on D. magna and C. dubia. The soil toxicity on collembolae and earthworms could be explained by 4 PAH congeners-fluorene, phenanthrene, pyrene, and fluoranthene. Yet, toxicity of the cokery soil as a whole was much lower than toxicity that could be deduced from the concentration of each congener in spiked soils, indicating that pollutants in the soil became less bioavailable with ageing.

Eisenia fetida increased removal of polycyclic aromatic hydrocarbons from soil

The removal of phenanthrene, anthracene and benzo(a)pyrene added at three different concentrations was investigated with or without earthworms (Eisenia fetida) within 11 weeks. Average anthracene removal by the autochthonous micro-organisms was 23%, 77% for phenanthrene and 13% for benzo(a)pyrene, while it was 51% for anthracene, 47% for benzo(a)pyrene and 100% for phenanthrene in soil with earthworms. At 50 and 100mg phenanthrene kg(-1)E. fetida survival was 91% and 83%, but at 150 mg kg(-1) all died within 15 days. Survival of E. fetida in soil amended with anthracene < or = 1000 mg kg(-1) and benzo(a)pyrene < or = 150 mg kg(-1) was higher than 80% and without weight loss compared to the untreated soil. Only small amounts of PAHs were detected in the earthworms. It was concluded that E. fetida has the potential to remove large amounts of PAHs from soil, but more work is necessary to elucidate the mechanisms involved.

Bioaccumulation and elimination of avermectin B1a in the earthworms (Eisenia fetida)

The acute toxicity, bioaccumulation, and elimination of avermectin B1a (AVM B1a) in earthworm (Eisenia fetida) were investigated in different exposure systems. The LC50 of AVM B1a on earthworms were 24.1 mg/kg and 17.1 mg/kg, respectively, for 7 and 14 days in artificial soil. The LC50 tested by the filter paper for 2 days was 4.63 microg/cm2. The earthworms were cultivated in artificial soil containing 0.6 mg/kg and 3.0 mg/kg AVM B1a, respectively for bioaccumulation experiments. The AVM B1a residues in earthworms were determined with HPLC-fluorescence method. The results showed that AVM B1a was taken up from the concentrated artificial soil by the earthworms and the steady-state levels were reached after 9-18 days of exposure. On the 18th day, the final concentrations of AVM B1a in the earthworms treated with two different dosages were 107 ng/g and 165 ng/g, respectively; there were not significantly accumulation. About 80.0% and 94.8% of the accumulated AVM B1a were eliminated respectively in two groups within 1 day after they were exposed to AVM B1a-free soil, but a trace amount of AVM B1a was found for a relative long time in earthworms.

The power of size. 1. Rate constants and equilibrium ratios for accumulation of organic substances related to octanol-water partition ratio and species weight

Most of the thousands of substances and species that risk assessment has to deal with are not investigated empirically because of financial, practical, and ethical constraints. To facilitate extrapolation, we have developed a model for accumulation kinetics of organic substances as a function of the octanol-water partition ratio (Kow) of the chemical and the weight, lipid content, and trophic level of the species. The ecological parameters were obtained from a previous review on allometric regressions. The chemical parameters, that is, resistances that substances encounter in water and lipid layers of organisms, were calibrated on 1,939 rate constants for absorption from water for assimilation from food and for elimination. Their ratio was validated on 37 laboratory bioconcentration and biomagnification regressions and on 2,700 field bioaccumulation data. The rate constant for absorption increased with the hydrophobicity of the substances with a Kow up to about 1,000 and then leveled off, decreasing with the weight of the species. About 39% of the variation was explained by the model, while deviations of more than a factor of 5 were noted for labile, large, and less hydrophobic molecules as well as for algae, mollusks, and arthropods. The efficiency for assimilation of contaminants from food was determined mainly by the food digestibility and thus by the trophic level of the species. A distinction was made between substances that are stable, that is, with a minimum elimination only, and those that are labile, that is, with an excess elimination probably largely due to biotransformation. The rate constant for minimum elimination decreased with the hydrophobicity of the substance and the weight of the species. About 70% of the variation was explained by the model, while deviations of more than a factor of 5 were noted for algae, terrestrial plants, and benthic animals. Labile substances were eliminated faster than isolipophilic stable compounds, but differences in laboratory elimination and accumulation were small compared with those in field accumulation. Excess elimination by vertebrates was faster than by invertebrates. Differences between terrestrial and aquatic species were attributed to water turnover rates, whereas differences between trophic levels were due to the food digestibility. Food web accumulation, expressed as organism-organic solids and organism-food concentrations ratios could be largely explained by ecological variables only. The model is believed to facilitate various types of scientific interpretation as well as environmental risk assessment.

Modelling the accumulation of hydrophobic organic chemicals in earthworms : Application of the equilibrium partitioning theory

In this paper a method is developed which can be used to estimate the body burden of organic hydrophobic chemicals in earthworms. In contrast to the equilibrium partitioning theory, two routes of uptake are incorporated: uptake from interstitial water and dietary uptake. Although many uncertainties still remain, calculations show that for earthworms steady state body burdens are mainly determined by uptake from interstitial water. Under most circumstances, the contribution of dietary uptake is small, except for hydrophobic chemicals (log Kow > 5) in soils with a high organic matter (OM) content of ≈ 20 %. Under those conditions, estimates of the steady state body burden calculated with the equilibrium partitioning model, in which only uptake from interstitial water is taken into account, might result in a small underestimation of the real body burden of chemicals in earthworms.