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

No effect of selected engineered nanomaterials on reproduction and survival of the springtail Folsomia candida

Although the number of studies on engineered nanomaterial (NM) toxicity to soil invertebrates is increasing, only a few studies have reported toxicity of NMs to soil dwelling model species, such as the invertebrate Folsomia candida. The main objective of this study was to determine the toxicity of five different engineered NMs (WCCo, CuO, Fe2O3, organic pigment and MWCNTs) for the springtail F. candida. Copper(ii), cobalt and iron chlorides were taken as positive controls. A standardized OECD test was used to measure effects on reproduction and survival, and toxicity was related to metal concentrations in soil and pore water. None of the NMs exerted adverse effects on springtail reproduction and survival at concentrations up to 6400 mg per kg dry soil, whereas the Cu, Co and Fe chlorides resulted in 50% decline in springtail reproduction at 981, 469 and 569 mg metal ion per kg dry soil, respectively. The absence of toxicity of the NMs could partly be explained by the low porewater metal concentrations, suggesting low solubility or slow solubilisation. The fate of engineered NMs in soil is rather complex but needs better understanding to facilitate predicting exposure of soil organisms

Phenotypic and transcriptional responses associated with multi-generation exposure of Folsomia candida to engineered nanomaterials

Sublethal effects of toxicants may cumulate over time and become apparent only when test organisms are exposed for multiple generations. In this study we determined phenotypic effects and transcriptional responses in the parthenogenetic soil invertebrate Folsomia candida over four generations, followed by two generations of recovery. Animals were exposed to two metal-based nanomaterials (NMs): copper oxide (CuO) and tungsten carbide–cobalt (WCCo), both homogenously mixed in with the soil. Survival and reproduction were not affected in any of four consecutive generations of F. candida exposed to CuO-NM at concentrations as high as 6400 mg Cu per kg dry LUFA 2.2 soil. WCCo-NM affected reproduction and survival from the third generation onwards, with EC50 values between 2400 and 5600 mg NM per kg dry soil, but recovery was seen in recovery generations 1 and 2 when kept in clean soil. Histological investigations showed that WCCo-NM (3200 mg kg−1) induced tissue damage and loss of villi from the gut epithelial cells. Expression of four target genes known to be responsive to stress were investigated by quantitative PCR at different exposure levels and in different generations. Expression of all genes was significantly affected by NMs even though exposures were below toxic threshold concentrations. In addition, gene expression did not always return to control levels during consecutive recovery over two generations in clean soil. This shows that gene expression assays can detect physiological alterations cumulating from one generation to the next initially without visible effects on phenotypic variables such as reproduction. The possibility of multi-generation carry-over of sublethal toxicity needs more attention in environmental risk assessment

Aging reduces the toxicity of pristine but not sulphidised silver nanoparticles to soil bacteria

In the environment engineered nanoparticles (ENPs) are subject to chemical and physical transformation processes. Thus, to understand their impact, it is important to consider how bioavailability and toxicity are influenced by these “aging” transformations with relation to environmental conditions and ENP properties. Here, two soil bacteria were exposed to Ag ENPs in ISO media (± fulvic acid) and soil pore water extracts with pH 6 and pH 8. The ENPs tested were 49 nm unfunctionalised, citrate stabilised (Ag-citr), 58 nm PVP-coated (Ag-PVP) and 36 nm sulphidised (Ag2S-PVP); AgNO3 was used as a positive control. Exposures were carried out using pristine (unaged) and 24 h aged ENPs, and the 24 h soluble fraction. Overall, toxicity was ranked AgNO3 > Ag-PVP ≥ Ag-citr ≫ Ag2S. Aging of AgNO3, Ag-PVP and Ag-citr in the ISO medium caused little change from unaged exposures and growth inhibition was mainly caused by soluble silver. Added fulvic acid decreased silver toxicity after aging and reduced the contribution of dissolution; as was the case in the soil pore waters where toxicity could not be attributed to ionic silver. Ag2S toxicity to A. globiformis in both ISO variants increased after aging, yet followed the same patterns as the metallic ENPs in the pore waters. For all ENPs pH effects were species dependent. Together this data showed that aging reduced toxicity in media with organic matter and despite soluble silver being the main driver of pristine ENP toxicity in the standard ISO medium, dissolution did not fully explain toxicity in the presence of organic matter

Lanthanum toxicity to five different species of soil invertebrates in relation to availability in soil

This study determined the toxicity of lanthanum, one of the most commonly used rare earth elements (REEs), to five representative soil invertebrates after 3–4 weeks exposure. Toxicity was related to total, 0.01 M CaCl2-extractable and porewater concentrations in the standard LUFA 2.2 soil, and for earthworms also to body concentrations. La sorption to LUFA 2.2 soil, estimated by relating total soil concentrations to CaCl2-extractable or porewater concentrations seemed to reach saturation at >1000 mg La/kg dry soil. Isopod (Porcellio scaber) growth was the most sensitive endpoint, followed by earthworm (Eisenia andrei), enchytraeid (Enchytraeus crypticus), springtail (Folsomia candida) and oribatid mite (Oppia nitens) reproduction, with EC50s of 312 (95% confidence interval: 5.6–619), 529 (295–762), 1010 ((>377 < 3133), 1220 (1180–1250) and 1500 (1250–1750) mg La/kg dry soil, respectively. EC50s related to CaCl2-extractable concentrations ranged between 1.3 (0.046–2.6) and 15.6 (5.6–25.7) mg La/kg dry soil, while porewater-based EC50s were 3.5 (−) and 10.2 (−) mg/L for the springtails and mites, respectively. La uptake in the earthworms linearly increased with increasing exposure concentration with bioaccumulation factors ranging between 0.04 and 0.53 (average ± SE: 0.24 ± 0.032). EC50 for effects on earthworm reproduction related to internal concentrations was 184 (61–301) mg La/kg dry body weight. A risk assessment based on the available toxicity for soil invertebrates, bacteria and plants resulted in an HC5 of approx. 50 mg La/kg dry soil, suggesting that La may affect soil ecosystems at concentrations slightly above natural background levels (6.6–50 mg La/kg dry soil) in non-polluted soils

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

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

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