Acute toxicity and bioaccumulation of common urban metals in Bombus impatiens life stages.

Metal contamination is ubiquitous in urban areas and represents a risk to arthropod species. Bees are exposed to metals while foraging within contaminated landscapes from multiple sources. Eliminating the risk of bee exposure to metals is complex, and requires an understanding of how bees become contaminated, how metals accumulate within bee bodies, and how this exposure influences their health. We selected Bombus impatiens, the common eastern bumble bee, as our focal species because it is the most frequently encountered bumble bee species in the eastern United States and common within urban greenspaces. The aims of this study were to quantify the lethal concentration exposure limit (LC50) for B. impatiens foragers, assess the bioaccumulation ability of environmentally relevant concentrations of common urban metals in adults, larvae, and pupae, and compare the LC50 values against field relevant concentrations collected by foraging bumble bees within a legacy city. Bumble bees were orally exposed to arsenic oxide, cadmium chloride, or chromium oxide in sucrose solution to encourage consumption. The LC50 for arsenic (As2O3 36.4 mg/L), cadmium (CdCl2 10.3 mg/L), and chromium (CrO3 189.6 mg/L) are 202×, 79×, and 1459× greater than concentrations found within urban bumble bee collected provisions, respectively. Adult bumble bees fed field realistic concentrations of metals accumulate significant amounts of cadmium and lead within their bodies, but do not accumulate chromium and arsenic. Additionally, adults accumulate significantly higher concentrations of metals than brood. While bumble bee foragers are unlikely to encounter lethal metal concentrations while foraging in contaminated landscapes, it is crucial to consider and understand how sublethal concentrations impact overall colony functioning. The results from this study highlight the need to identify hazards and bioaccumulation ability of common metals as bees respond differently to each metal species, as well as the impacts of metal mixtures on bioaccumulation and toxicity.

Using solid-phase microextraction during ultrasound reveals higher aqueous PAHs release from contaminated sediment.

Ultrasound (US) releases polycyclic aromatic hydrocarbons (PAHs) from contaminated creosote sediments and degrades PAHs in aqueous solution. However, it is unclear how much PAHs release occurs during active US compared to after US is stopped. In this study, solid-phase microextraction (SPME) was used to determine aqueous PAH concentrations desorbed from Little Scioto River creosote contaminated sediment during exposure to 20 kHz ultrasound (US) at a power of 430 W L-1. First, SPME fiber-water partition coefficients,KSPME, were experimentally determined and shown to be comparable with previous studies. Next, PAH concentrations released into aqueous solution were determined by sequentially exposing fresh, conditioned SPME fibers in a reactor containing the contaminated sediment and DI for 10 min periods. Three consecutive 10 min periods each were measured during US and after US. Compared to mixing only, PAHs desorbed during ultrasound was significantly higher. In addition, for phenanthrene, anthracene, and fluoranthene, US showed significantly higher aqueous concentrations during US compared with after US. For these less soluble PAHs, desorption into the aqueous phase reaches and surpasses expected equilibrium aqueous concentrations. However, when US is ceased, PAHs appear to resorb onto sediment resulting in the lower concentrations measured in these PAH compounds after US that are similar to expected equilibrium aqueous concentrations. Typical analytical extraction methods for determining the effects of US require stopping treatment and may underestimate the potential US has for release of contaminants from sediment during US. Using SPME during US treatment reveals that the concentration of PAHs during US may surpass the expected equilibrium aqueous concentration of some PAHs congeners. To our knowledge, this higher concentration observed during US compared to after US has not been shown previously.

Tolerance of glacial-melt stoneflies (Plecoptera) and morphological responses of chloride cells to stream salinity.

Aquatic insects within glacial-melt streams are adapted to low dissolved inorganic ion concentrations. Increases in ion concentrations in glacial-melt streams are predicted with increasing air temperatures, which may impact future aquatic insect survival in these streams. We hypothesized that stonefly (Plecoptera) naiads from glacial-melt streams acclimated to different conductivity would differ in survival, median lethal concentrations, and chloride cell responses to elevated conductivity above that expected in our study streams. We conducted field bioassays in remote glacial-melt streams in southwestern China in 2015 and exposed representative stonefly naiads (Chloroperlidae, Nemouridae, Taeniopterygidae) from stream sites differing in conductivity to experimental conductivity ranging from 11 to 20,486 µS/cm for up to 216 h. We examined survivorship, calculated 96-h median lethal concentrations, and measured chloride cell responses with scanning electron microscopy. Chloroperlidae survival after 120 and 216 h did not differ (P > 0.05) among conductivity treatments. The combined Nemouridae/Taeniopterygidae survival after 120 and 216 h was the least (P < 0.05) in conductivity treatments >16,349 µS/cm. Taeniopterygidae survival after 120 h was also the least (P < 0.05) in conductivity treatments >16,349 µS/cm. The 96-h median lethal concentrations did not differ (P > 0.05) between the combined Nemouridae/Taeniopterygidae group (2306 µS/cm) and Taeniopterigydae (2002 µS/cm) and were lower (P < 0.05) than the 96-h median lethal concentration for Chloroperlidae (8167 µS/cm). Chloroperlidae caviform cell number, density, and area decreased (P < 0.05) with increasing conductivity. Taeniopterygidae caviform cell count decreased (P < 0.05) with increasing conductivity, but cell density and area did not. Chloroperlidae and Taeniopterygidae coniform cell characteristics and Nemouridae bulbiform cell characteristics were not affected by conductivity. Our results suggest that Chloroperlidae, Nemouridae, and Taeniopterygidae from glacial-melt streams in China may be able to tolerate moderate increases in conductivity (i.e., 100 to 200 µS/cm).

Solvent choice influences final toxicity results in Thamnocephalus platyurus bioassay when exposed to microcystin -LR.

Cyanobacterial blooms present a threat to many waterbodies around the world used for drinking water and recreational purposes. Toxicology tests, such as the Thamnotoxkit-F which uses the cladoceran T. platyurus, have been employed to assess the health hazards that these blooms may pose to the public. However, reported median lethal concentrations (LC50) of microcystin -LR to T. platyurus vary significantly from one study to the next. The variation in solvent type and concentrations used to dissolve microcystin -LR in preparation for toxicity experiments may be contributing to the variations in LC50 values found in the literature. The primary goal of this study was to determine what solvents and their corresponding concentrations can be used for microcystin -LR testing using T. platyurus without artifactually impacting LC50 values. All toxicity testing was completed using glassware as polystyrene containers have been shown to sorb microcystin. Microcystin -LR LC50 values for T. platyurus were determined using United States Environmental Protection Agency (US EPA) moderately hard standard freshwater as a control for comparison with systems that were prepared using dimethyl sulfoxide or methanol to dissolve microcystin -LR. Low levels of dimethyl sulfoxide (2%) or methanol (1%) did not impact LC50 values of microcystin -LR to T. platyurus compared to US EPA moderately hard standard freshwater diluted in microcystin -LR. However, higher levels of dimethyl sulfoxide (4%) and methanol (1.4% and 4%) did lower the LC50 for microcystin -LR to T. platyurus, consistent with the toxicity of these solvents to T. platyurus when dosed in the absence of microcystin -LR. Researchers need to report the type and concentrations of solvents used in toxicity tests using cyanotoxins in order to ensure that results can be intercompared appropriately. Furthermore, researchers need to use caution when using organic solvents such as dimethyl sulfoxide or methanol to ensure that these solvents are not causing significant mortality in toxicity testing.

Bioavailability and Ecotoxicity of Lead in Soil: Implications for Setting Ecological Soil Quality Standards.

Ecological soil quality standards for lead (Pb) that account for soil Pb bioavailability have not yet been derived. We derived such standards based on specific studies of the long-term bioavailability and toxicity of Pb to soil organisms and a compilation of field data on the bioaccumulation of Pb in earthworms. Toxicity thresholds of Pb to plants, invertebrates, or microorganisms vary over more than 2 orders of magnitude, and the lowest values overlap with the range in natural Pb background concentrations in soil. Soils freshly spiked with Pb2+ salts exhibit higher Pb bioavailability and lower toxic thresholds than long-term aged and leached equivalents. Comparative toxicity tests on leaching and aging effects suggest using a soil Pb threshold that is 4.0 higher, to correct thresholds of freshly spiked soils. Toxicity to plants and earthworms, and microbial N-transformation and bioaccumulation of Pb in earthworms increase with decreasing effective cation exchange capacity (eCEC) of the soil, and models were derived to normalize data for variation of the eCEC among soils. Suggested ecological quality standards for soil expressed as total soil Pb concentration are lower for Pb toxicity to wildlife via secondary poisoning compared with direct Pb toxicity to soil organisms. Standards for both types of receptors vary by factors of approximately 4 depending on soil eCEC. The data and models we have collated can be used for setting ecological soil quality criteria for Pb in different regulatory frameworks. Environ Toxicol Chem 2021;40:1950-1963. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessing the Ecological Risks of Per- and Polyfluoroalkyl Substances: Current State-of-the Science and a Proposed Path Forward.

Per- and poly-fluoroalkyl substances (PFAS) encompass a large, heterogenous group of chemicals of potential concern to human health and the environment. Based on information for a few relatively well-understood PFAS such as perfluorooctane sulfonate and perfluorooctanoate, there is ample basis to suspect that at least a subset can be considered persistent, bioaccumulative, and/or toxic. However, data suitable for determining risks in either prospective or retrospective assessments are lacking for the majority of PFAS. In August 2019, the Society of Environmental Toxicology and Chemistry sponsored a workshop that focused on the state-of-the-science supporting risk assessment of PFAS. The present review summarizes discussions concerning the ecotoxicology and ecological risks of PFAS. First, we summarize currently available information relevant to problem formulation/prioritization, exposure, and hazard/effects of PFAS in the context of regulatory and ecological risk assessment activities from around the world. We then describe critical gaps and uncertainties relative to ecological risk assessments for PFAS and propose approaches to address these needs. Recommendations include the development of more comprehensive monitoring programs to support exposure assessment, an emphasis on research to support the formulation of predictive models for bioaccumulation, and the development of in silico, in vitro, and in vivo methods to efficiently assess biological effects for potentially sensitive species/endpoints. Addressing needs associated with assessing the ecological risk of PFAS will require cross-disciplinary approaches that employ both conventional and new methods in an integrated, resource-effective manner. Environ Toxicol Chem 2021;40:564-605. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Toward Sustainable Environmental Quality: Priority Research Questions for North America.

Anticipating, identifying, and prioritizing strategic needs represent essential activities by research organizations. Decided benefits emerge when these pursuits engage globally important environment and health goals, including the United Nations Sustainable Development Goals. To this end, horizon scanning efforts can facilitate identification of specific research needs to address grand challenges. We report and discuss 40 priority research questions following engagement of scientists and engineers in North America. These timely questions identify the importance of stimulating innovation and developing new methods, tools, and concepts in environmental chemistry and toxicology to improve assessment and management of chemical contaminants and other diverse environmental stressors. Grand challenges to achieving sustainable management of the environment are becoming increasingly complex and structured by global megatrends, which collectively challenge existing sustainable environmental quality efforts. Transdisciplinary, systems-based approaches will be required to define and avoid adverse biological effects across temporal and spatial gradients. Similarly, coordinated research activities among organizations within and among countries are necessary to address the priority research needs reported here. Acquiring answers to these 40 research questions will not be trivial, but doing so promises to advance sustainable environmental quality in the 21st century. Environ Toxicol Chem 2019;38:1606-1624. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Effects of Soil Properties on the Toxicity and Bioaccumulation of Lead in Soil Invertebrates.

The present study examined the effects of soil physical and chemical properties on the toxicity of lead (Pb) to earthworms (Eisenia fetida) and collembolans (Folsomia candida), and on bioaccumulation of Pb by earthworms, in soils amended with Pb salts. Toxicity tests were conducted in 7 soils varying in soil properties (pH 4.7-7.4, effective cation exchange capacity [eCEC] 4-42 cmolc /kg, organic carbon 10-50 g C/kg) that were leached and pH corrected after spiking with PbCl2 . The median effect concentrations (EC50s) based on total soil Pb concentrations ranged from 35 to 5080 mg Pb/kg for earthworms and 389 to >7190 mg/kg for Collembola. Significant positive correlations were observed between log (EC50) for earthworm reproduction and log (eCEC, total C, exchangeable Ca and Mg, or clay content), but no significant correlations were observed between Pb toxicity to Collembola and soil properties. Expressing Pb dose as either the free ion (Pb2+ ) activity in porewater or as the measured dissolved porewater concentration of Pb did not explain differences in toxicity among soils. The bioaccumulation factors (BAFs) for Pb in earthworms ranged up to >10-fold across 6 soil treatments, with a median of 0.16, and the BAF was significantly correlated with eCEC (p = 0.038, r = -0.84), but not with any other soil properties. Soil properties related to eCEC (total C, exchangeable Ca and Mg, clay content) had a significant effect on Pb toxicity and bioaccumulation in earthworms, but no relationship was found for Collembola. As a major soil property affecting the bioavailability of Pb, CEC should be incorporated into any soil hazard assessment of Pb as a modifying factor of toxicity and bioaccumulation for earthworms. Environ Toxicol Chem 2019;38:1486-1494. © 2019 SETAC.

Ecological impacts of fluridone and copper sulphate in catfish aquaculture ponds.

Fluridone and copper sulphate are often used for controlling macrophytes and algae in aquaculture ponds. The present study examined the ecological effects of these chemicals on macrophyte, phytoplankton, and zooplankton biomass; plankton community structure; water quality parameters; and fish survival and yield in catfish culture ponds using a randomized complete block design. The estimated half-life of fluridone in the individual ponds ranged from 1.6 d to 10.8 d. Free copper ion activity in ponds treated with copper sulphate was dynamic, ranging from pCu of 7.7 to 8.9 after each application and decreasing to approximately 12 (1 × 10(-12) M) within 1 wk after each application, approaching observed values in control ponds (pCu = 12.3-13.4). No difference in macrophyte biomass was observed among treatments. Fluridone and copper treatments elicited different responses within the phytoplankton community. Copper treatments reduced Cyanophyta biomass but increased biomass of more tolerant taxa among the Chlorophyta and Chrysophyta. Fluridone treatments reduced total phytoplankton biomass including Cyanophyta and increased the sensitivity of Chlorophyta and Chrysophyta to copper. Copper also affected zooplankton community composition as a result of direct toxic effects on sensitive zooplankton taxa (e.g., Cladocera), whereas Copepoda biomass in copper-treated ponds exceeded that in controls. Catfish survival and yield were not significantly different among treatments. The results of the present study suggest that fluridone and copper interact at realistic application rates, increasing the ability to control algae compared with treatments where they are applied alone.

Toxicity in lead salt spiked soils to plants, invertebrates and microbial processes: Unraveling effects of acidification, salt stress and ageing reactions.

The fate and effects of toxic trace metals in soil freshly spiked soluble metal salts do not mimic those of metals in the field. This study was set up to test the magnitude of effects of salinity, acidification, and ageing on toxicity of lead (Pb) to plants, invertebrates and soil microbial processes. Three soils were spiked with Pb2+ salts up to a concentration of 8000 mg Pb/kg and were tested either after spiking, after soil leaching followed by pH correction, or after a 5-year outdoor ageing period with free drainage followed by pH correction. Soil solution ionic strength exceeded 150 mmol/L in soils tested directly after spiking and this decreased partially after leaching and returned back to background values after 5-year outdoor equilibration. Chronic toxicity to two plants, two invertebrates, and three microbial endpoints was consistently found in all spiked soils that were not leached. This toxicity significantly decreased or became absent after 5 years of ageing in 19 of the 20 toxicity tests by a factor 8 (median factor; range: 1.4->50), measured by the factor increase of total soil Pb dose required to induce 10% inhibition. The toxicity of Pb in leached soils was intermediate between the other two treatments. The lowest detectable chronic thresholds (EC10) in aged soils ranged 350-5300 mg Pb/kg. Correlation analysis, including data of Pb2+ speciation in soil solution, suggests that reduced ionic strength rather than acidification or true ageing is the main factor explaining the soil treatment effects after spiking. It is suggested that future toxicity studies should test fine PbO powder as a relevant source for Pb in soils to exclude the confounding salt effects.

Soil properties affect the toxicities of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to the enchytraeid worm Enchytraeus crypticus.

The authors investigated individual toxicities of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to the potworm Enchytraeus crypticus using the enchytraeid reproduction test. Studies were designed to generate ecotoxicological benchmarks that can be used for developing ecological soil-screening levels for ecological risk assessments of contaminated soils and to identify and characterize the predominant soil physicochemical parameters that can affect the toxicities of TNT and RDX to E. crypticus. Soils, which had a wide range of physicochemical parameters, included Teller sandy loam, Sassafras sandy loam, Richfield clay loam, Kirkland clay loam, and Webster clay loam. Analyses of quantitative relationships between the toxicological benchmarks for TNT and soil property measurements identified soil organic matter content as the dominant property mitigating TNT toxicity for juvenile production by E. crypticus in freshly amended soil. Both the clay and organic matter contents of the soil modulated reproduction toxicity of TNT that was weathered and aged in soil for 3 mo. Toxicity of RDX for E. crypticus was greater in the coarse-textured sandy loam soils compared with the fine-textured clay loam soils. The present studies revealed alterations in toxicity to E. crypticus after weathering and aging TNT in soil, and these alterations were soil- and endpoint-specific.

Differential acute toxicity of tetrachlorobenzene isomers to oligochaetes in soil and water: application of the critical body residue concept.

The acute, lethal potency of the 1,2,3,4-, 1,2,4,5- and 1,2,3,5-tetrachlorobenzene isomers was compared in the terrestrial and aquatic oligochaetes Eisenia andrei and Tubifex tubifex. 1,2,4,5-TeCB was neither lethal, nor produced any perceptible adverse effects, at lipid normalized concentrations predicted to be lethal according to the well-established critical body residue concept. If a narcotic is defined as a substance capable of inducing narcosis, rather than a substance displaying certain physical or chemical properties (e.g., log K(ow)), then we do not believe these findings challenge the critical body residue because by the former definition, 1,2,4,5-tetrachlorobenzene is not a narcotic.

Application of the tissue residue approach in ecological risk assessment.

The objective of this work is to present a critical review of the application of the tissue residue approach (TRA) in ecological risk and/or impact assessment (ERA) of chemical stressors and environmental criteria development. A secondary goal is to develop a framework for integrating the TRA into ecological assessments along with traditional, exposure concentration-based assessment approaches. Although widely recognized for its toxicological appeal, the utility of the TRA in specific applications will depend on numerous factors, such as chemical properties, exposure characteristics, assessment type, availability of tissue residue-response data, and ability to quantify chemical exposure. Therefore, the decision to use the TRA should include an evaluation of the relative strengths, limitations, and uncertainties among exposure and residue-based methods for characterizing toxicological effects. Furthermore, rather than supplanting exposure concentration-based toxicity assessments, the TRA can be highly effective for evaluating and reducing uncertainty when used in a complementary manner (e.g., when evaluating multiple lines of evidence in field studies). To address limitations with the available tissue residue-response data, approaches for extrapolating residue-based toxicity data across species, tissues, and exposure durations are discussed. Some of these approaches rely on predicted residue-response relationships or toxicological models that have an implicit residue-response basis (e.g., biotic ligand model). Because risk to an organism is a function of both its exposure potential and inherent sensitivity (i.e., on a residue basis), bioaccumulation models will be required not only for translating tissue residue criteria into corresponding water and sediment criteria, but also for defining the most vulnerable species in an assemblage (i.e., highly exposed and highly sensitive species). Application of the TRA in ecological assessments and criteria development are summarized for bioaccumulative organic chemicals, TBT, and in situ bioassays using bivalve molluscs.

Uptake kinetics and subcellular compartmentalization of cadmium in acclimated and unacclimated earthworms (Eisenia andrei).

Acclimation to cadmium (Cd) levels exceeding background concentrations may influence the ability of earthworms to accumulate Cd with minimum adverse effects. In the present study, earthworms (Eisenia andrei) were acclimated by exposure to 20 mg/kg Cd (dry wt) in Webster soil for 28 d. A 224-d bioaccumulation test was subsequently conducted with both acclimated and unacclimated worms exposed in Webster soils spiked with 20 mg/kg and 100 mg/kg Cd (dry wt). Uptake kinetics and subcellular compartmentalization of Cd were examined. Results suggest that acclimated earthworms accumulated more Cd and required a longer time to reach steady state than unacclimated worms. Most of the Cd was present in the metallothionein (MT) fraction. Cadmium in the MT fraction increased approximately linearly with time and required a relatively longer time to reach steady state than Cd in cell debris and granule fractions, which quickly reached steady state. Cadmium in the cell debris fraction is considered potentially toxic, but low steady state concentrations observed in the present study would not suggest the potential for adverse effects. Future use of earthworms in ecological risk assessment should take into consideration pre-exposure histories of the test organisms. A prolonged test period may be required for a comprehensive understanding of Cd uptake kinetics and compartmentalization.

Determining exposure dose in soil: the effect of modifying factors on chlorinated benzene toxicity to earthworms.

This study describes the comparison of multiple approaches for estimating the median lethal concentration of selected chlorinated benzenes (CBs) from an homologous series yielding acute toxicity to the earthworm Eisenia andrei in Webster soil. The coefficients of variation were significantly lower for solid-phase microextraction (SPME), tissue residue, and hexane-extractable based CB exposure estimates compared to nominal CB exposure estimates. The range of CB exposure estimates based on SPME, tissue residue, or nominal was narrower than lethal concentration exposure estimates based on hexane-extractable CBs. Despite the insignificant difference between the coefficients of variation for SPME and hexane-extractable based measures of CB exposure, the results of this study suggest that the use of SPME based estimates of exposure may improve the accuracy of ecological risk assessment when used an alternative to hexane-extractable (total soil CBs) due to a narrower range of medial lethal concentrations when comparing equipotent compounds.

Evaluating the contribution of soil properties to modifying lead phytoavailability and phytotoxicity.

Soil properties affect Pb bioavailability to human and ecological receptors and should be considered during ecological risk assessment of contaminated soil. We used path analysis (PA) to determine the relative contribution of soil properties (pH, organic C [OC], amorphous Fe and Al oxides [FEAL], and cation-exchange capacity [CEC]) in modifying Pb bioavailability. The response of biological endpoints (bioaccumulation and dry matter growth [DMG]) of lettuce (Lactuca sativa) grown on 21 Pb-spiked (2,000 mg/kg) soils were determined. Lettuce tissue Pb ranged from 3.22 to 233 mg/kg, and relative DMG ranged from 2.5 to 88.5% of their respective controls. Simple correlation showed strong relationships between CEC and OC (p < 0.01) and weaker relationships between pH and FEAL (p < 0.05) and Pb bioaccumulation. Results of PA suggest that soil pH increased the negative surface charge of organic matter and clay, thereby increasing CEC and decreasing Pb bioaccumulation. Also, the direct effect of OC on tissue Pb can be attributed to formation of surface Pb complexes by organic matter functional group ligands. Increased OC and/or CEC reduced Pb solubility and bioavailability in the 21 soils in the present study. The relative importance of soil properties likely will vary between studies employing different soils. Soil properties should be considered during the ecological risk assessment of metal in contaminated soils. Path analysis is useful for ecological studies involving soils with a wide range of physicochemical properties and can assist in site risk assessment of metals and remediation decisions on contaminated sites.

Effect of soil properties on lead bioavailability and toxicity to earthworms.

Soil properties are important factors modifying metal bioavailability to ecological receptors. Twenty-one soils with a wide range of soil properties (USA; http://soils.usda.gov/technical/classification/taxonomy/) were amended with a single concentration of Pb (2,000 mg/kg) to determine the effects of soil properties on Pb bioavailability and toxicity to earthworms. Earthworm mortality ranged from 0 to 100% acute mortality following exposure to the same total concentration of Pb (2,000 mg/kg) in amended field soils. Internal Pb concentrations in earthworms ranged from 28.7 to 782 mg/kg, with a mean of 271 mg/kg. Path analysis was used to partition correlations in an attempt to discern the relative contribution of each soil property. Results of path analysis indicated that pH was the most important soil property affecting earthworm mortality (p < 0.01) and internal Pb (p < 0.05). Soil pH was related inversely to mortality and internal Pb, soil solution Pb, and Pb bioavailability. The most important soil property modifying reproduction was amorphous iron and aluminum oxides (FEAL). Because FEAL is rich in pH-dependent cation-exchange sites, several soil properties, including pH, FEAL, and cation-exchange capacity, have a causal effect on Pb adsorption and soluble Pb. Path analysis is useful for assessing contaminated soils with a wide range of soil properties and can assist in ecological risk assessment and remediation decisions for contaminated sites. Soil properties are important factors modifying metal bioavailability and toxicity and should be considered during the ecological risk assessment of metals in contaminated soils.

Biological significance of metals partitioned to subcellular fractions within earthworms (Aporrectodea caliginosa).

Metal ions in excess of metabolic requirements are potentially toxic and must be removed from the vicinity of important biological molecules to protect organisms from adverse effects. Correspondingly, metals are sequestrated in various forms, defining the accumulation pattern and the magnitude of steady-state levels reached. To investigate the subcellular fractions over which Ca, Mg, Fe, Cu, Zn, Cd, Pb, Ni, and As are distributed, earthworms (Aporrectodea caliginosa) collected from the field were analyzed by isolating metal-rich granules and tissue fragments from intracellular microsomal and cytosolic fractions (i.e., heat-stable proteins and heat-denatured proteins). The fractions showed metal-specific binding capacity. Cadmium was mainly retrieved from the protein fractions. Copper was equally distributed over the protein fraction and the fraction comprising tissue fragments, cell membranes, and intact cells. Zinc, Ca, Mg, and As were mainly found in this fraction as well. Lead, Fe, and Ni were mainly isolated from the granular fraction. To study accumulation kinetics in the different fractions, three experiments were conducted in which earthworms were exposed to metal-spiked soil and a soil contaminated by anthropogenic inputs and, indigenous earthworms were exposed to field soils. Although kinetics showed variation, linear uptake and steady-state types of accumulation patterns could be understood according to subcellular compartmentalization. For risk assessment purposes, subcellular distribution of metals might allow for a more precise estimate of effects than total body burden. Identification of subcellular partitioning appears useful in determining the biological significance of steady-state levels reached in animals.

Reduction in acute toxicity of soils to terrestrial oligochaetes following the removal of bioavailable polycyclic aromatic hydrocarbons with mild supercritical carbon dioxide extraction.

Three soil samples contaminated with polycyclic aromatic hydrocarbons (PAHs) that caused 100% mortality to terrestrial oligochaetes were extracted with supercritical carbon dioxide to remove the bioavailable fraction of PAHs. Although the remaining PAH concentrations were high after supercritical fluid extraction (SFE), 650 to 8,000 mg/kg, acute toxicity to Eisenia fetida and Enchytraeus albidus essentially was eliminated. These results demonstrate that mild SFE with pure carbon dioxide preferentially extracts PAH molecules that are bioavailable toxicologically to the oligochaetes, although biologically unavailable PAHs are not extracted, suggesting that SFE could be used for the removal of toxicity due to hydrophobic organic chemicals in soils during toxicity identification evaluations.