Toxicokinetics and toxicodynamics of Ag nanomaterials (NM300K) in the soil environment-impact on Enchytraeus crypticus (Oligochaeta).

Silver (Ag) is one of the most used elements in the nanomaterials (NMs) form, which upon release to the environment can be harmful to organisms. We compared the toxicokinetics (TK) and toxicodynamics (TD) of Ag from AgNO3 (0, 15, 45, 135, 405 mg Ag/kg soil) and AgNM300K (0, 75, 150, 300, 600, 1200 mg Ag/kg soil) in the model organism Enchytraeus crypticus. Organisms were exposed in LUFA 2.2 soil, and besides body Ag concentrations, survival and reproduction were determined, in a time series (for 21 days). In the soil, the available (CaCl2 extractable) Ag fraction from Ag NM300K increased from 0 to 21 days but did not consistently change for AgNO3. Internal concentrations reached equilibrium in most exposures to both Ag forms. The organisms were able to internalize and eliminate Ag, but less when exposed to Ag NM300K. The overall uptake rate constants for Ag from AgNO3 and Ag NM300K exposures were 0.05 and 0.06 kg soil/kg organism/day, respectively, the elimination rate constants 0.2 and 0.1 day-1, respectively. For AgNO3 the median lethal concentrations decreased steadily with time, while for Ag NM300K they remained constant during the first 10 days of exposure followed by a 2-fold decline in the last 7 days. The 21-d LC50s for both Ag forms were similar but the LC50inter (based on internal concentrations) were 63 and 121 mg Ag/kg body DW (Dry Weight) for AgNO3 and Ag NM300K, respectively, showing higher toxicity of AgNO3. These results show the importance of assessing time to toxicity, a relevant factor in toxicity assessment, especially for NMs.

Toxicokinetics and toxicodynamics of copper and cadmium in the soil invertebrate Enchytraeus crypticus (Oligochaeta).

The aim of this study was to evaluate the toxicokinetics-toxicodynamics (TKTD) of Cu and Cd in the soil model organism Enchytraeus crypticus, and assess the development of internal effect concentrations over time. Animals were exposed in LUFA 2.2 soil spiked with increasing concentrations of Cu and Cd. Survival, reproduction and internal metal concentrations in the animals were evaluated at different points in time over a period of 21 days. Internal concentrations increased with time, for Cu reaching a steady state after c. 10 days, except for the highest test concentration, and for Cd continuing to increase after 21 days. Applying a one-compartment model to all data together, estimated uptake and elimination rate constants for Cu and Cd were 0.08 and 0.45 kg soil/kg organism/day and 0.4 and 0.04 per day, respectively. Median lethal concentrations, based on total soil concentrations, decreased with time for Cu and did not reach a steady state level, but they did not change with time for Cd. The LC50inter (based on internal concentrations) was 75 mg Cu/kg body DW and > 800 mg Cd/kg body weight. Animals were able to regulate Cu internal concentrations, keeping them low, while for Cd internal concentrations continued to increase showing lack of regulation and also the importance of exposure time. This study highlights the advantages of using a TKTD approach to understand the relation between organism survival and internal Cu or Cd concentrations over time.

Dose-dependent effects of lead and cadmium and the influence of soil properties on their uptake by Helix aspersa: an ecotoxicity test approach.

Three soil types with different physicochemical properties were selected to evaluate their effect on lead and cadmium bioavailability and toxicity in the land snail Helix aspersa. In 28-day ecotoxicity tests, H. aspersa juveniles were exposed to increasing concentrations of Pb or Cd. EC50s, concentrations reducing snail growth by 50%, differed between the soils and so did Cd and Pb uptake in the snails. For lead, EC50s were 2397-6357 mg Pb/kg dry soil, while they ranged between 327 and 910 mg Cd/kg dry soil for cadmium. Toxicity and metal uptake were highest on the soil with the lowest pH, organic matter content and Cation Exchange Capacity (CEC). Growth reduction was correlated with metal accumulation levels in the snails' soft body, and differences in toxicity between the soils decreased when EC50s were expressed on the basis of internal metal concentrations in the snails. These results confirm the effect of soil properties; pH, CEC, OM content, on the uptake and growth effect of Pb and Cd in H. aspersa, indicating the importance of properly characterizing soils when assessing the environmental risk of metal contaminated sites.

Assessing the toxicity of thiamethoxam, in natural LUFA 2.2 soil, through three generations of Folsomia candida.

In the field, long-term exposure is a rule rather than an exception. As a consequence, the relatively short-term standard toxicity tests may not be adequate for assessing long-term effects of pesticide exposure. This study determined the toxicity of the neonicotinoid thiamethoxam, both pure and in the formulation Actara® (25% active substance), to the springtail Folsomia candida, over three generations (P, F1 and F2). For the parental generation (P), the toxicity of pure thiamethoxam and Actara® did not differ significantly, with LC50s and EC50s of 0.32-0.35 and 0.23-0.25 mg a.s./kg dry soil, respectively. For the F1 and F2 generations, LC50s were >0.37 mg a.s./kg dry soil for both compounds. Actara was more toxic towards reproduction in the F1 generation (EC50 0.16 mg a.s./kg dry soil) than pure thiamethoxam (EC50 0.23 mg a.s./kg dry soil). For generation F2, there was no significant difference in the toxicity of the compounds towards reproduction, with EC50s of >0.37 and 0.30 mg a.s./kg dry soil for Actara® and pure thiamethoxam respectively. These results suggest a slight decrease in the toxicity of the compounds throughout the generations tested. The similarity in the toxicity of pure and formulated thiamethoxam indicates that the ingredients in the formulation Actara® do not enhance toxicity.

Comparative toxicity of imidacloprid and thiacloprid to different species of soil invertebrates.

Neonicotinoid insecticides have come under increasing scrutiny for their impact on non-target organisms, especially pollinators. The current scientific literature is mainly focused on the impact of these insecticides on pollinators and some aquatic insects, leaving a knowledge gap concerning soil invertebrates. This study aimed at filling this gap, by determining the toxicity of imidacloprid and thiacloprid to five species of soil invertebrates: earthworms (Eisenia andrei), enchytraeids (Enchytraeus crypticus), Collembola (Folsomia candida), oribatid mites (Oppia nitens) and isopods (Porcellio scaber). Tests focused on survival and reproduction or growth, after 3-5 weeks exposure in natural LUFA 2.2 standard soil. Imidacloprid was more toxic than thiacloprid for all species tested. F. candida and E. andrei were the most sensitive species, with LC50s of 0.20-0.62 and 0.77 mg/kg dry soil for imidacloprid and 2.7-3.9 and 7.1 mg/kg dry soil for thiacloprid. EC50s for effects on the reproduction of F. candida and E. andrei were 0.097-0.30 and 0.39 mg/kg dry soil for imidacloprid and 1.7-2.4 and 0.44 mg/kg dry soil for thiacloprid. The least sensitive species were O. nitens and P. scaber. Enchytraeids were a factor of 5-40 less sensitive than the taxonomically related earthworm, depending on the endpoint considered. Although not all the species showed high sensitivity to the neonicotinoids tested, these results raise awareness about the effects these insecticides can have on non-target soil invertebrates.

Multigeneration toxicity of imidacloprid and thiacloprid to Folsomia candida.

In a recent study, we showed that the springtail Folsomia candida was quite sensitive the neonicotinoid insecticides imidacloprid and thiacloprid. This study aimed at determining the toxicity of both compounds to F. candida following exposure over three generations, in natural LUFA 2.2 standard soil. In the first generation, imidacloprid was more toxic than thiacloprid, with LC50s of 0.44 and 9.0 mg/kg dry soil, respectively and EC50s of 0.29 and 1.5 mg/kg dry soil, respectively. The higher LC50/EC50 ratio suggests that thiacloprid has more effects on reproduction, while imidacloprid shows lethal toxicity to the springtails. In the multigeneration tests, using soil spiked at the start of the first generation exposures, imidacloprid had a consistent effect on survival and reproduction in all three generations, with LC50s and EC50s of 0.21-0.44 and 0.12-0.29 mg/kg dry soil, respectively, while thiacloprid-exposed animals showed clear recovery in the second and third generations (LC50 and EC50 > 3.33 mg/kg dry soil). The latter finding is in agreement with the persistence of imidacloprid and the fast degradation of thiacloprid in the test soil.

Toxicity of Pb contaminated soils to the oribatid mite Platynothrus peltifer.

To understand the toxicity of Pb-polluted shooting fields, oribatid mites Platynothrus peltifer were exposed to shooting field soils containing 47-2398 mg Pb/kg dry weight (DW) and having pH(CaCl2) 3.2-6.8 and 3.8-13% organic matter (OM). Exposures also included artificial soils with different pH and OM contents as well as two natural soils used as controls. Exposures lasted for 2 (acute) and 12 weeks (chronic). Survival, reproduction and uptake of Pb in the mites were related to total, water-extractable and 0.01 M CaCl2-extractable and porewater Pb concentrations as well as soil characteristics. After both the acute and chronic exposures, adult survival was not significantly affected, while upon chronic exposure reproduction was remarkably reduced in the acidic forest soils with Pb concentrations ≥2153 mg/kg DW and pH(CaCl2) ≤ 3.5. P. peltifer juvenile numbers were significantly negatively and internal Pb concentrations in the mites were significantly positively related with total, extractable and porewater Pb concentrations. This study shows that P. peltifer is not very sensitive to Pb and therefore may not be a suitable indicator of Pb-polluted soils.

Multigenerational exposure of Ag materials (nano and salt) in soil - environmental hazards in Enchytraeus crypticus (Oligochaeta).

Because of its properties, silver is among the most used metals both as salt and as nanomaterials (NMs), hence reaching the environment. Multigenerational (MG) exposure testing is scarce, and especially so for NMs and soil invertebrates. In this study the MG effects of Ag NMs (Ag NM300K) and Ag salt (AgNO3) were assessed, using Enchytraeus crypticus in LUFA 2.2 soil. Survival, reproduction and internal Ag concentration in the animals were measured throughout 7 generations (5 generations (F0-F4) in spiked soil plus 2 (F5-F6) in clean soil) exposed to sublethal concentrations corresponding to the reproduction EC10 and EC50 obtained in standard toxicity tests (45 and 60 mg Ag per kg soil DW for AgNO3; 20 and 60 mg Ag per kg soil DW for Ag NM300K). MG exposure caused a dose-related decrease in reproduction for both Ag forms. Ag uptake peaked in the F1 (64 days) for AgNO3 and F2 (96 days) for Ag NM300K, after which it decreased. In agreement with toxicokinetic studies, a maximum body Ag concentration was reached (20 mg Ag per kg body DW (AgNO3) and 70 mg Ag per kg body DW (Ag NM300K)) and after which detoxification mechanisms seem to be activated with elimination of Ag accompanied by a decrease in reproduction. Transfer to clean soil allowed Ag to be (fully) eliminated from the animals. This MG study confirmed the effects determined in standard reproduction toxicity tests but further allowed to monitor the dynamics between exposure and effects of the Ag materials, and how the animals seem to cope with Ag for 7 generations by compensating between detoxification and reproductive output.

Persistence of chironomids in metal polluted andean high altitude streams: does melanin play a role?

In high altitude Andean streams an intense solar radiation and coinciding metal pollution allow the persistence of only a few specialized taxa, including chironomids. The aim of the present study was therefore to determine the mechanisms underlying the persistence of chironomids under these multiple stress conditions, hypothesizing that melanin counteracts both the adverse effects of solar radiation and of metals. Melanin was determined in chironomids from reference and metal polluted streams at 3000 and 4000 m altitude, being 2-fold higher at 4000 m compared to 3000 m, and 2-fold higher in polluted streams than in reference streams at both altitudes. The field observations were experimentally verified by assessing the combined effects of Cu and UV-B on the survival and melanin concentration in larvae of the model species Chironomus riparius (Chironomidae, Diptera). In laboratory exposures, the highest melanin concentrations were found in larvae surviving toxic Cu concentrations, but not in those exposed to the highest UV-B radiation. Pre-exposure to UV-B decreased the sensitivity of the larvae to UV-B and to Cu+UV-B. It is concluded that in the field, melanin may protect chironomids partially against both elevated metal concentrations and solar radiation, allowing them to persist under the harshest conditions in high altitude streams.

Toxicokinetics and toxicodynamics of chromium in the soil invertebrate Enchytraeus crypticus (Oligochaeta).

Chromium emissions led to increased concentrations in soil, where it can affect soil organisms to relevant levels. With the aim of better understanding the effects of Cr throughout time, its toxicokinetics-toxicodynamics (TKTD) were evaluated in the soil model organism Enchytraeus crypticus to assess the development of internal concentrations and consequent toxic effects. To achieve this goal, organisms were exposed in LUFA 2.2 soil spiked with increasing CrCl3 concentrations. During the 21-day exposure period, survival, internal concentrations, and reproduction were evaluated at several time points up to 21 days. Uptake and elimination rate constants were 0.0044 kg soil/kg organism/day and 0.023 per day, respectively. Internal Cr concentrations increased with time, generally reaching equilibrium within 14 days with an estimated LC50inter (based on internal metal concentrations) of 57.7 mg Cr/kg body DW. Internal Cr concentrations were regulated by the organisms up to exposure to 360 mg Cr/kg soil DW, where the elimination rate was highest, but at 546 mg Cr/kg soil DW the animals were no longer able to eliminate Cr, and the internal concentrations were well above the estimated LC50inter. At day 21, exposure to 546 mg Cr/kg soil DW significantly reduced survival by 23 %, while reproduction EC50 was 344 mg Cr/kg soil DW. This study highlights the advantages of using a TKTD approach to understand the development of internal metal concentrations in time and relate it to the phenotypical effects observed. Toxicity is better understood when also taking into account time and not just exposure concentration alone.

Microarthropod communities act as functional mediators of ecosystem recovery in abandoned metal(loid) mine tailings in semiarid areas.

Abandoned metal(loid) mine tailings show inhospitable conditions for the establishment of above- and below-ground communities (e.g., high metal(loid) levels, organic matter and nutrient deficiency). This worsens in semiarid areas due to the harsh climate conditions. Fertility islands (vegetation patches formed by plants that spontaneously colonize the tailings) can serve as potential nucleation spots fostering beneficial plant-microbial interactions. However, less attention has been paid to the soil invertebrates living beneath these patches and their functional role. Here, we studied whether the spontaneous plant colonization of abandoned metal(loid) mine tailings led to a greater presence of soil microarthropod communities and whether this could contribute to improving ecosystem functionality. Microarthropods were extracted, taxonomically identified and subsequently assigned to different functional groups (saphrophages, omnivores, predators) in bare soils and differently vegetated patches within metalliferous mine tailings and surrounding forests in southeast Spain. Microarthropod communities were significantly different in bare soils compared with vegetated patches in mine tailings and surrounding forests. Plant colonization led to an increase in microarthropod abundance in tailing soils, especially of mites and springtails. Moreover, saprophages and omnivores, but not predators, were favored in vegetated patches. The initial microarthropod colonization was mainly linked to higher organic matter accumulation and greater microbial activity in the vegetated patches within mine tailings. Moreover, soil formation processes already initiated in the tailings were beneficial for soil biota establishment. Thus, below-ground communities created an anchorage point for plant communities by primarily starting heterotrophic activities in the vegetated patches, thereby contributing to recover ecosystem functionality.

Toxicokinetics of silver and silver sulfide nanoparticles in Chironomus riparius under different exposure routes.

Engineered nanoparticles released into surface water may accumulate in sediments, potentially threatening benthic organisms. This study determined the toxicokinetics in Chironomus riparius of Ag from pristine silver nanoparticles (Ag NPs), a simulating aged Ag NP form (Ag2S NPs), and AgNO3 as an ionic control. Chironomid larvae were exposed to these Ag forms through water, sediment, or food. The potential transfer of Ag from larvae to adult midges was also evaluated. Results revealed higher Ag uptake by C. riparius upon exposure to Ag2S NPs, while larvae exposed to pristine Ag NPs and AgNO3 generally presented similar uptake kinetics. Uptake patterns of the different Ag forms were generally similar in the tests with water or sediment exposures, suggesting that uptake from water was the most important route of Ag uptake in both experiments. For the sediment bioaccumulation test, uptake was likely a combination of water uptake and sediment particles ingestion. Ag uptake via food exposure was only significant for Ag2S NPs. Ag transfer to the terrestrial compartment was low. In our environmentally relevant exposure scenario, chironomid larvae accumulated relatively high Ag concentrations and elimination was extremely low in some cases. These results suggest that bioaccumulation of Ag in its nanoparticulate and/or ionic form may occur in the environment, raising concerns regarding chronic exposure and trophic transfer. This is the first study determining the toxicokinetics of NPs in Chironomus, providing important information for understanding chironomid exposure to NPs and their potential interactions in the environment.

Toxicokinetics of Chromium in Enchytraeus crypticus (Oligochaeta).

Chromium is naturally occurring, but emission from anthropogenic sources can lead to increased soil concentrations. Information on its toxicokinetics is essential in order to understand the time needed to reach toxicity and the mechanisms of uptake/elimination. In this study the toxicokinetics of Cr(III) was evaluated using the soil standard species Enchytraeus crypticus. The animals were exposed to 180 mg Cr/kg dry soil, a sublethal concentration, in LUFA 2.2 natural soil. OECD guideline 317 was followed, with a 14-day uptake phase in spiked soil followed by a 14-day elimination in clean soil. Exposure to Cr led to fast uptake and elimination, with Ku = 0.012 kgsoil/kgorganism/day and Ke = 0.57 day-1. The bioaccumulation factor was 0.022, and DT50 for elimination was 1.2 days. The concentration of Cr reached an internal equilibrium in the animals after 10 days. Transfer to clean soil allowed body Cr concentrations to return to background levels after approximately 7 days. E. crypticus seemed able to efficiently regulate internal Cr concentrations by actively eliminating Cr (an essential element). Although Ku and Ke deviated from the values reported in other studies for other soil invertebrates, the bioaccumulation factors were similar. These findings show the importance of toxicokinetic studies in evaluating toxicity based on internal metal concentrations that can more accurately represent the bioavailable concentration.

Effects of sulfidation of silver nanoparticles on the Ag uptake kinetics in Brassica rapa plants.

Land application of sewage sludge containing increasing levels of silver nanoparticles (AgNPs) raises concerns about the risk for plant exposure. This study compared the uptake kinetics and distribution of Ag in Brassica rapa seedlings grown in Lufa 2.2 natural soil spiked with 20 nm Ag2S NPs, with those from 3 to 8 nm AgNPs, 50 nm AgNPs and AgNO3 exposures (10 mg Ag/kg dry soil). A two-compartment model was used to describe the uptake kinetics of Ag in plants, distinguishing two stages: stage I with increasing Ag uptake followed by stage II with decreasing Ag uptake. The concentration of Ag in roots from Ag2S NPs was about 14 and 10 times lower than for the other AgNPs and AgNO3 exposures, respectively, at the end of stage I, with root translocation rate constants being higher for Ag2S NPs. In stage II, Ag uptake occurred only for the 50 nm AgNPs. The distribution of Ag in B. rapa exposed to pristine, ionic and sulfidized AgNPs differed at the end of exposure. This study shows that Ag uptake and distribution in plants depends on the Ag form in soil, highlighting the importance of studying the environmentally relevant chemical species in NPs risk assessment.

Bioaccumulation but no biomagnification of silver sulfide nanoparticles in freshwater snails and planarians.

Bioaccumulation studies are critical in regulatory decision making on the potential environmental risks of engineered nanoparticles (NPs). The present study evaluated the toxicokinetics of silver, taken up from sulfide nanoparticles (Ag2S NPs; simulating an aged Ag NP form) and AgNO3 (ionic counterpart), in the pulmonate snail Physa acuta and the planarian Girardia tigrina. The snails were first exposed for 7 days to Ag-spiked water, along with the microalgae Raphidocelis subcapitata upon which they fed setting up a double route exposure, and subsequently provided as pre-exposed food to the planarians. Ag toxicokinetics and bioaccumulation were assessed in planarians and snails, and potential biomagnification from snail to planarian was evaluated. Gut depuration was also explored to understand whether it constitutes a factor likely to influence Ag toxicokinetics and internal concentrations in the test species. Both species revealed Ag uptake in Ag2S NP and AgNO3 treatments, with higher uptake from the latter. Uptake by the snails was probably via a combination of water exposure and ingested algae provided as food, but ingestion of algae possibly had higher relevance for Ag uptake from the Ag2S NPs compared to AgNO3. For planarians, diet probably was the most important exposure route since no Ag uptake was observed in previous waterborne exposures to Ag2S NPs. Kinetics and internal Ag concentrations did not significantly differ between depurated and non-depurated snails or planarians. The planarians fed on snails revealed no biomagnification. To the best of our knowledge this is the first study investigating the toxicokinetics and biomagnification of NPs in planarians, and with that providing important data on the kinetics and bioaccumulation of NPs in a relevant benthic species.

Field mixtures of currently used pesticides in agricultural soil pose a risk to soil invertebrates.

Massive use of pesticides in conventional agriculture leads to accumulation in soil of complex mixtures, triggering questions about their potential ecotoxicological risk. This study assessed cropland soils containing pesticide mixtures sampled from conventional and organic farming systems at La Cage and Mons, France. The conventional agricultural field soils contained more pesticide residues (11 and 17 versus 3 and 11, respectively) and at higher concentrations than soils from organic fields (mean 6.6 and 10.5 versus 0.2 and 0.6 µg kg-1, respectively), including systemic insecticides belonging to neonicotinoids, carbamate herbicides and broad-spectrum fungicides mostly from the azole family. A risk quotient (RQi) approach evaluated the toxicity of the pesticide mixtures in soil, assuming concentration addition. Based on measured concentrations, both conventional agricultural soils posed high risks to soil invertebrates, especially due to the presence of epoxiconazole and imidacloprid, whereas soils under organic farming showed negligible to medium risk. To confirm the outcome of the risk assessment, toxicity of the soils was determined in bioassays following standardized test guidelines with seven representative non-target invertebrates: earthworms (Eisenia andrei, Lumbricus rubellus, Aporrectodea caliginosa), enchytraeids (Enchytraeus crypticus), Collembola (Folsomia candida), oribatid mites (Oppia nitens), and snails (Cantareus aspersus). Collembola and enchytraeid survival and reproduction and land snail growth were significantly lower in soils from conventional compared to organic agriculture. The earthworms displayed different responses: L. rubellus showed higher mortality on soils from conventional agriculture and large body mass loss in all field soils, E. andrei showed considerable mass loss and strongly reduced reproduction, and A. caliginosa showed significantly reduced acetylcholinesterase activity in soils from conventional agriculture. The oribatid mites did not show consistent differences between organic and conventional farming soils. These results highlight that conventional agricultural practices pose a high risk for soil invertebrates and may threaten soil functionality, likely due to additive or synergistic "cocktail effects".

Life cycle responses of the midge Chironomus riparius to compounds with different modes of action.

Compounds with different modes of action may affect life cycles of biota differently. The aim of the present study was therefore to investigate the impact of four chemicals with different modes of action, including the essential metal copper, the nonessential metal cadmium, the organometal tributyltin, and the polycyclic aromatic compound phenanthrene, on chronic lethal and sublethal life-cycle effect parameters of the nonbiting midge Chironomus riparius, applying a 28-day sediment toxicity test. Tributyltin and cadmium delayed emergence significantly over a wide range of sublethal concentrations, while this range was narrow for copper and almost absent for phenanthrene. The chronic LC50/LOECEmT50 ratio, expressing these differences, amounted to 1.5, 3.5, 12.0, and 18.2 for respectively phenanthrene, copper, cadmium, and tributyltin. Thus the more specific the compounds mode of action, the higher the chronic LC50/LOECEmT50 ratio, as previously observed for acute-to-chronic ratios (ACRs). Comparison of our results with literature derived LC50/LOEC ratios showed a comparable trend and a lower variability compared to ACRs. We therefore conclude that the presently proposed chronic ratio is indicative for the specificity of a chemicals mode of action and that it is less variable than the ACR.

The influence of soil properties on the toxicity of molybdenum to three species of soil invertebrates.

Mo toxicity to earthworms (Eisenia andrei), Collembola (Folsomia candida) and enchytraeids (Enchytraeus crypticus) was determined in 10 European soils and a standard artificial soil, freshly spiked with Na(2)MoO(4), after 28 days exposure. Mo affected survival only in three low pH sandy soils; in all other soils LC50 was >3200 mg Mo/kg dry soil. EC50 values for the reproduction toxicity of Mo were 129-2378 mg/kg for earthworms, 72->3396 mg/kg for Collembola, and 301->2820 mg/kg for enchytraeids. Variation in toxicity among soils could not be explained by differences in available (pore water, water and 0.01 M CaCl(2) extractable) Mo concentrations. Clay content best predicted the EC50 for Mo toxicity to earthworms, while toxicity of Mo for enchytraeids was best described by soil pH. For Collembola no relationships could be derived due to the absence of toxicity in most soils. Soil properties had a strong but species-specific effect on Mo toxicity to soil invertebrates.

Toxicity in Neonicotinoids to Folsima candida and Eisenia andrei.

We compared the toxicity of the neonicotinoids imidacloprid, thiacloprid, thiamethoxam, acetamiprid, and clothianidin in terms of the survival and reproduction of 2 species of soil invertebrates, Folsomia candida and Eisenia andrei. Tests were performed using LUFA 2.2 natural soil, following standard protocols aimed at answering 2 questions: 1) Is there a difference in the toxicity between pure compound and its formulation? and 2) Is there a difference in the sensitivity of the species exposed to the same compound? For E. andrei, formulations and pure compounds had similar toxicity to both endpoints tested. For F. candida, acetamiprid and imidacloprid had different toxicities, with acetamiprid being 4 times more toxic to survival (median lethal concentration [LC50] 0.12 mg active substance [a.s.]/kg dry soil) and imidacloprid being 4 times more toxic to reproduction of the springtail (median effect concentration [EC50] 0.25 mg a.s./kg dry soil) than their commercial formulations. The most toxic compound to E. andrei was acetamiprid (LC50 0.80 and EC50 0.35-0.40 mg a.s./kg), and the most toxic to F. candida was clothianidin (LC50 0.07 and EC50 0.05 mg a.s./kg). Estimated risk ratios indicated that only one application/yr of clothianidin in the formulation Poncho® may pose a threat to the populations of springtails and earthworms. Environ Toxicol Chem 2020;39:548-555. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Effect of soil properties on Pb bioavailability and toxicity to the soil invertebrate Enchytraeus crypticus.

The present study investigated the bioavailability and toxicity of lead to the potworm Enchytraeus crypticus in six soils with different properties. Pb partitioning between the soil solution and solid phase was affected by soil organic matter (OM) content, cation exchange capacity (CEC) and water holding capacity (WHC). After 21 d exposure, Pb bioaccumulation in the enchytraeids was positively correlated with total soil Pb concentration. Bioaccumulation was best predicted by Pb availability (CaCl2-extractable and porewater Pb concentrations), and by the Ca concentration in pore water and the CEC of the soils. Toxicity varied greatly among soils, with LC50s and EC50reproductions based on total Pb concentrations ranging from 246 to >3092 and from 81 to 1008 mg Pb/kg dry soil, respectively. The variation in LC50s among soils was explained by differences in CaCl2-extractable Pb concentrations in soil and internal Pb concentrations in the animals. The differences in EC50reproductions could be explained from the CaCl2-extractable Pb concentrations in the soils. Although it was also correlated with CEC and porewater Ca concentration, pHCaCl2 was the dominating factor for predicting Pb toxicity based on total soil concentrations. This study demonstrates that soil properties, such as pH, CEC and Ca concentration in pore water, significantly affected the bioavailability and toxicity of Pb and therefore should be taken into account when assessing the ecological risk of metals in contaminated soils.