Comparison of earthworm and chemical assays of the bioavailability of aged 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, and heavy metals in orchard soils

Single and combined effects of phenanthrene and cadmium on oxidative stress and detoxification related biomarkers in clams (Meretrix meretrix)

Biomarkers concerning antioxidant reactions and detoxification metabolics were evaluated in Meretrix meretrix exposed to cadmium (Cd, 10 μg/L) and phenanthrene (PHE, 100 μg/L) individually and in combination (10 μg/L Cd + 100 μg/L PHE) for 7 days. The accumulation of Cd and PHE measured in the digestive gland, gill, mantle, and axe foot of the clam showed significant increase in combination treatment and it was higher than the single Cd or single PHE treatment. The activities of oxidative stress-related enzymes, the expression of Cu/Zn SOD, and the content of MDA increased after Cd and PHE exposure in the digestive gland and gill at most cases. In the digestive gland, CAT gene expression was significantly induced in Cd-single group and significantly inhibited in PHE-single group and Cd-PHE mixed group at both day 3 and day 7; in the gill, CAT gene expression was significantly inhibited in all groups at day 3 and except for Cd-single group at day 7. MT expression was significantly induced in Cd-single and Cd-PHE mixed groups at day 7, while hsp70 expression was significantly inhibited in PHE-single and Cd-PHE mixed groups at day 7. The results indicated that SOD, CAT, GST, MDA, Cu/Zn SOD, CAT, MT and hsp70 were sensitive to cadmium and PHE in a water environment, and can be used as indicators of marine heavy metal pollution.

Effect of salinity on the toxicokinetics, oxidative stress, and metallothionein gene expression in Meretrix meretrix exposed to cadmium

To understand the effect of salinity on the toxicokinetics, oxidative stress, and detoxification of cadmium-exposed Meretrix meretrix, M. meretrix were acclimatized to different salinities (8, 14, 20, 26, and 32 ppt) for 14 d, exposed to 10 μg/L Cd for 7 d, followed by a 28-day depuration period. The internal Cd concentration was determined, and the activities of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), and glutathione-S-transferase (GST)), and the malondialdehyde (MDA) content were measured. The mRNA expression levels of antioxidant enzyme (Cu/Zn SOD, CAT) and detoxification-related genes metallothionein (MT) were analyzed. The mean concentrations of Cd in M. meretrix tissues were in the order gill > digestive gland > mantle > axe foot. The Cd uptake rate in the four tissues decreased with increasing salinity (range: 14-26 ppt). The Cd elimination half-lives were the highest at 8 ppt and 14 ppt salinity. Cadmium activated the four oxidative stress-related related enzymes in the gills. At the end of accumulation period, Cd exposure at 20 ppt salinity significantly increased the expression of Cu/Zn SOD. CAT expression was significantly inhibited at 20 ppt salinity, but was induced at 32 ppt. MT mRNA expression was only induced under Cd at 20 ppt salinity. At the end of depuration period, Cu/Zn SOD expression was inhibited at salinities of 8, 14, and 26 ppt. The results indicated that SOD, CAT, GST, MDA, Cu/Zn SOD, CAT, and MT were sensitive to cadmium in a water environment, and can be used as indicators of marine heavy metal pollution.

Enantioselectivity of new chiral triazole fungicide mefentrifluconazole: Bioactivity against phytopathogen, and acute toxicity and bioaccumulation in earthworm (Eisenia fetida)

Elaborating the environmental behavior of mefentrifluconazole, a novel triazole fungicide, in stereoselective level is of paramount importance for the application of the pesticide in agriculture. In this study, the enantioselective bioactivity, acute toxicity and stereoselective bioaccumulation of mefentrifluconazole in earthworm (Eisenia fetida) were investigated. Bioactivity tests against four pathogens revealed that R-(-)-mefentrifluconazole exhibited approximately 11-113 times higher bioactivity than its S-(+)-mefentrifluconazole. However, the LC₅₀ of S-(+)-, rac- and R-(-)-mefentrifluconazole to earthworm was measured to be 4.1, 11.4 and 7.3 μg/cm², respectively, indicating active ingredient R-(-)-mefentrifluconazole is less toxic than its racemate and S-form. Accumulation of mefentrifluconazole in earthworms was non-enantioselective and negatively related to its adsorption onto soils. The concentration of mefentrifluconazole in in situ pore water (C_IPW) and CaCl₂ extraction (C_CaCl2) was closely related to its accumulation in earthworms, suggesting that C_IPW and C_CaCl2 could be appropriate indicators for estimation of the bioavailability of mefentrifluconazole in soil. Conclusively, our study provides necessary information for the risk assessment of mefentrifluconazole in agriculture.

Effect of temperature on the toxicokinetics and gene expression of the pacific cupped oyster Crassostrea gigas exposed to cadmium

In this study, we investigated the influence of temperature on the bioaccumulation and depuration of Crassostrea gigas exposed to Cd associated with its molecular responses. Oysters were acclimatized to different temperatures (10 °C, 15 °C, 20 °C, 25 °C, and 30 °C) for 14 d and then exposed to 10 μg/L Cd for 28 d, followed by a depuration period of 35 d. Oysters were sampled for chemical analysis by inductively coupled plasma mass spectrometry (ICP-MS) and for mRNA quantification by qPCR. In the digestive gland, gill, and mantle, the cadmium concentration at 10 °C was significantly lower than that at 25 °C and 30 °C in both the whole experiments. The use of a two-compartment model showed that the uptake rate k₁ in the above three tissues increased with increasing temperatures ranging from 15 to 25 °C. The fastest elimination rates and shortest half-lives were observed at 15-25 °C. The induction of metallothionein (MT) only occurred in the digestive gland at 15 °C and 20 °C at the end of the accumulation phase. In the mantle and gills, the expression of P-glycoprotein (P-gp) was significantly induced at the end of the accumulation phase and significantly inhibited at the end of the depuration phase. In the digestive gland, the expression of P-gp was induced at the end of both the accumulation and depuration phases. Heat shock protein (hsp70) expression exhibited an overall increasing trend throughout the experiment.

Continuing Persistence and Biomagnification of DDT and Metabolites in Northern Temperate Fruit Orchard Avian Food Chains

Dichlorodiphenyldichlorethane (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane) (DDT) is an organochlorine insecticide that was widely used from the late 1940s to the 1970s in fruit orchards in the Okanagan valley, British Columbia, Canada, and in the process, contaminated American robin (Turdus migratorius) food chains with the parent compound and metabolite dichlorodiphenyldichloroethylene (1,1-dichloro-2,2-bis(4-chlorophenyl)ethylene) (p,p'-DDE). In the present study, we examined the biological fate of these DDT-related (DDT-r) compounds at the same sites/region 26 years after a previous study by: (1) collecting soil, earthworms, and American robin eggs from apple, cherry, and pear orchards; (2) characterizing the diet and trophic positions of our biota using stable isotope analyses of δ¹³ C and δ¹⁵ N; and (3) estimating fugacity, biota-soil-accumulation factors (BSAFs), and biomagnification factors (BMFs). Mean p,p'-DDE concentrations (soil: 16.1 µg/g organic carbon-lipid equivalent; earthworms: 96.5 µg/g lipid equivalent; eggs: 568 µg/g lipid equivalent) revealed that contamination is present at elevated levels similar to the 1990s and our average soil DDE:DDT ratio of 1.42 confirmed that DDT is slowly degrading. American robins appeared to feed at similar trophic levels, but on different earthworms as indicated by egg stable isotope values (mean δ¹⁵ N = 8.51‰ ± 0.25; δ¹³ C = -26.32‰ ± 0.12). Lumbricidae and Aporrectodea worms shared a roughly similar δ¹⁵ N value; however, Lumbricus terrestris showed a markedly enriched δ¹³ C isotope, suggesting differences in organic matter consumption and physiological bioavailability. Biota-soil-accumulation factors and BMFs ranged over several orders of magnitude and were generally >1 and our fugacity analyses suggested that p,p'-DDE is still thermodynamically biomagnifying in American robin food chains. Our results demonstrate that DDT-r in fruit orchards remains bioavailable to free-living terrestrial passerines and may pose a potential toxicological risk. Environ Toxicol Chem 2021;40:3379-3391. © 2021 Her Majesty the Queen in Right of Canada. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Environment and Climate Change Canada.

Soil dissipation and bioavailability to earthworms of two fungicides under laboratory and field conditions

The representativeness of laboratory studies of the fate of pesticides in soil in field conditions is questionable. This study aimed at comparing the dissipation and bioavailability to earthworms of two fungicides, dimoxystrobin (DMX) and epoxiconazole (EPX), over 12 months under laboratory and field conditions. In both approaches, the fungicides were applied to the same loamy soil as a formulated mixture at several concentrations. We determined total DMX and EPX concentrations in the soil using exhaustive extraction, their environmental availability using mild extraction and their bioavailability through internal concentrations in exposed earthworms. The initial fungicide application appeared as much better controlled in terms of dose and homogeneity in the laboratory than in the field. One year after application, a similar dissipation rate was observed between the laboratory and field experiments (ca 80% and 60% for DMX and EPX, respectively). Similarly, the ratio of available/total concentrations in soil displayed the same trend whatever the duration and the conditions (field or lab), EPX being more available than DMX. Finally, the environmental bioavailability of the two fungicides to earthworms was heterogeneous in the field, but, in the laboratory, the bioaccumulation was evidenced to be dose-dependent only for DMX. Our findings suggest that the actual fate of the two considered fungicides in the environment is consistent with the one determined in the laboratory, although the conditions differed (e.g., presence of vegetation, endogeic earthworm species). This study allowed better understanding of the fate of the two considered active substances in the soil and underlined the need for more research dedicated to the link between environmental and toxicological bioavailability.

Use of Zinc Carbonate Spiking to Obtain Phytotoxicity Thresholds Comparable to Those in Field-Collected Soils

Several studies have reported the presence of smithsonite (ZnCO₃ ) in soils polluted by zinc mining. The present study aimed to determine upper critical threshold values of Zn phytotoxicity in a substrate spiked with ZnCO₃ and to compare them with those obtained in field-collected soils. We studied Zn toxicity to perennial ryegrass (Lolium perenne L.) grown in pots with unpolluted peat treated with increasing concentrations of ZnCO₃ that produced nominal total Zn concentrations of 0, 0.7, 1.3, 2.0, 2.6, and 3.3%. To keep constant near-neutral pH value in all the treatments, we used decreasing concentrations of dolomitic lime. In the treatment with total soil Zn of 3.3% (pH 6.8), the foliar Zn concentration of L. perenne was 1914 ± 211 mg kg^-1 , falling into the range of 2400 ± 300 mg kg^-1 reported for Lolium species grown under similar laboratory conditions in a polluted soil (total soil Zn 5.4%, pH 7.3) collected near a Zn smelter. The value of 92 ± 98 mg kg^-1 was obtained for the median effective concentration (EC50) values of 0.01 M KNO₃ -extractable Zn using the responses of shoot dry biomass, shoot length, and total pigments. This value falls within the range of 95 ± 46 mg kg^-1 reported in other studies for the EC50 values of salt-extractable Zn using field-collected soils. The application of ZnCO₃ for spiking was able to mimic foliar Zn concentrations of Lolium species observed in field-collected soils. The effective concentrations of soil Zn obtained in the present study are comparable to those obtained in field-collected soils. Future research should determine effective concentrations of metals using soils spiked with metal-containing compounds that mimic a real source of contamination. Environ Toxicol Chem 2020;39:1790-1796. © 2020 SETAC.

Oxidative stress in the galaxiid fish, Galaxias maculatus, exposed to binary waterborne mixtures of the pro-oxidant cadmium and the anti-oxidant diclofenac

Chemical mixtures represent environmentally-realistic exposures of contaminants to aquatic biota. However, there remains a limited understanding of how toxicant mixtures may impact biological function, relative to their individual components. In the current study, oxidative stress responses of the freshwater galaxiid fish inanga (Galaxias maculatus) were examined following exposure to the pro-oxidant trace metal cadmium (2 or 9 μg L^-1), and the anti-oxidant pharmaceutical drug diclofenac (770 μg L^-1), individually or in simple binary mixtures. Cadmium exposure in the absence of diclofenac significantly decreased renal catalase activity, increased hepatic catalase activity, decreased renal superoxide dismutase (SOD) and decreased glutathione-S-transferase activity, effects that are suggestive of anti-oxidant defense inhibition and/or generation of increased reactive oxygen species. Diclofenac exposure in the absence of cadmium resulted in a decreased renal lipid peroxidation, consistent with its known anti-oxidant properties. The presence of waterborne diclofenac altered the effects of cadmium on catalase activity in the liver, SOD activity in the gill, and lipid peroxidation in the liver. Co-exposure with cadmium modulated diclofenac effects on lipid peroxidation in the kidney. These data indicate the capacity of each of these toxicants to offset biological effects of the other when both co-occur in urban waters at specific concentrations. This study also demonstrates the complexity of outcomes in contaminant mixtures, even when these stressors are presented as simple binary combinations.

Effects of waterborne cadmium on metabolic rate, oxidative stress, and ion regulation in the freshwater fish, inanga (Galaxias maculatus)

The freshwater fish Galaxias maculatus (inanga) is a widespread Southern hemisphere species, but despite its habitation of lowland near-coastal waters with a high potential for cadmium contamination, nothing is known regarding its sensitivity to this toxic trace metal. Acute (96h) exposures were therefore performed to determine sublethal responses of inanga to waterborne cadmium at a regulatory trigger value (nominally 0.2μgL^-1; measured 1μgL^-1), an environmental level (measured at 2.5μgL^-1), and an effect level (measured at 10μgL^-1). Whole body (tissue remaining following excision of kidney and liver) cadmium burden remained constant up until an exposure concentration of 10μgL^-1, at which point cadmium concentration increased significantly. A transient effect of cadmium on metabolic rate was observed, with an impaired oxygen consumption noted at 2.5, but not 1 or 10, μg L^-1. Cadmium did not impair influx rates of either sodium or calcium, and no effects of cadmium on oxidative stress parameters (catalase activity, lipid peroxidation) were noted in the kidney. However, at cadmium concentrations of 2.5 and 10μgL^-1, lipid peroxidation in the liver increased, concomitant with a decline in hepatic catalase activity. These data indicate that there are significant differences in the mechanisms of cadmium toxicity in inanga, relative to better-studied Northern hemisphere species, especially with respect to ionoregulatory impacts. However, effects were induced at cadmium concentrations unlikely to be encountered in any but the most highly contaminated waterways, and thus our data suggest that current trigger values for cadmium concentrations in Australian and New Zealand waters are likely to be protective of inanga.

Evaluation of a hollow fiber supported liquid membrane device as a chemical surrogate for the measurements of zinc (II) bioavailability using two microalgae strains as biological references

The environmental bioavailability of zinc (II), i.e., the uptake of the element by an organism, was determined using two microalgae species, Scenedesmus acutus and Pseudokirchneriella subcapitata, and estimated using hollow fiber supported liquid membrane (HF-SLM) device as the chemical surrogate. Several experimental conditions were studied including the presence of organic matter, inorganic anions and concomitant cations and pH. The results show strong positive correlation coefficients between the responses given by the HF-SLM and the microalgae species (r = 0.900 for S. acutus and r = 0.876 for P. subcapitata) in multivariate environments (changes in pH, calcium, humic and citrate concentrations). The maximum amount of zinc (II) retained by the HF-SLM (4.7 × 10^-8 mol/cm²) was higher than those for P. subcapitata and S. acutus (9.4 × 10^-11 mol/cm² and 6.2 × 10^-11 mol/cm², respectively). The variation in pH (pH 5.5-9) was the variable with the greatest effect on zinc internalization in all systems, increasing approximately 2.5 times for P. subcapitata and 5.5 times for S. acutus respect to pH = 5.5, while the presence of humic acids did not affect the response. The species' concentration analysis of the experimental design at pH = 5.5 indicated that the amount of internalized zinc (II) by the HF-SLM and both microalgae species is strongly dependent on the free zinc concentration (r = 0.910 for the HF-SLM, r = 0.922 for S. acutus and r = 0.954 for P. subcapitata); however, at pH = 9.0, the amount of internalized zinc (II) is strongly dependent on the sum of free zinc and labile species (r = 0.912 for the HF-SLM, r = 0.947 for S. acutus and r = 0.900 for P. subcapitata). The presence of inorganic ligands (chloride, sulfate, phosphate, carbonate, and nitrate) and metal ions (cobalt (II), copper (II), nickel (II), chromium (VI), lead (II) and cadmium (II)) produced different behaviors both in the chemical surrogate and the biological references. The results showed that the synthetic device can mimic biological uptake in the presence of humic acids, nitrate, sulfate, and phosphate, and pH within the range 5.5-9 when S. acutus was used as the biological reference, considering the simultaneous contribution of the Zn²⁺ and ZnOH⁺ labile species depending on the chemical composition of the medium.

Evaluation of epoxiconazole bioavailability in soil to the earthworm Aporrectodea icterica

In soil, the determination of total concentration using an exhaustive extraction method has little relevance to evaluate the exposure of an organism to a chemical, because of sorption processes. This study aims to propose a mild extraction method to evaluate the bioavailability of the fungicide epoxiconazole to the earthworm Aporrectodea icterica. Experiments were conducted in soils presenting various textures and organic carbon contents, spiked with formulated epoxiconazole 7 to 56 days prior to their extraction. In parallel, the epoxiconazole concentration was determined in exposed earthworms and the fungicide's effects were evaluated by measuring weight gain, enzymatic activities and total protein contents. Among the various mild chemical solvents tested to evaluate the environmental availability of the fungicide, the 50 mM hydroxypropyl-β-cyclodextrin solution allowed to extract around 30% of epoxiconazole. This percentage corresponded to the ratio determined in exposed A. icterica under similar soil conditions. Furthermore, this mild method was demonstrated to be sensitive to soil sorption capacities and to ageing. The mild extraction method was then applied to explore the relationship between total and (bio)available concentrations in soil and in A. icterica, over 7- or 28-day exposure time. This demonstrated the proportionality between epoxiconazole concentration in earthworm and available in soil (up to 96%, with regression coefficient R(2) = 0.98). Sublethal effects on earthworm remained not significant.

Mechanisms of zinc toxicity in the galaxiid fish, Galaxias maculatus

Zinc (Zn) is an essential metal, which is ubiquitous in aquatic environments occurring both naturally, and through anthropogenic inputs. This study investigated impacts of sub-lethal Zn exposure in the galaxiid fish Galaxias maculatus. Known as inanga, this amphidromous fish is widespread throughout the Southern hemisphere, but to date almost nothing is known regarding its sensitivity to elevated environmental metals. Fish were exposed to environmentally-relevant concentrations of Zn (control, 8, 270 and 1000μgL(-1)) over 96h. End-points measured included those relating to ionoregulatory disturbance (whole body calcium and sodium influx), oxygen consumption (respirometry), oxidative stress (catalase activity and lipid peroxidation) and whole body accumulation of Zn. Zn exposure caused increases in catalase activity and lipid peroxidation, but only at the highest exposure level tested. Zn also significantly inhibited calcium influx, but stimulated sodium influx, at 1000μgL(-1). The sub-lethal changes induced by Zn exposure in inanga appear to be conserved relative to other, better-studied species. These data are the first to explore the sensitivity of juvenile galaxiid fish to Zn, information that will be critical to ensuring adequate environmental protection of this important species.

Subcellular partitioning of metals in Aporrectodea caliginosa along a gradient of metal exposure in 31 field-contaminated soils

Subcellular fractionation of metals in organisms was proposed as a better way to characterize metal bioaccumulation. Here we report the impact of a laboratory exposure to a wide range of field-metal contaminated soils on the subcellular partitioning of metals in the earthworm Aporrectodea caliginosa. Soils moderately contaminated were chosen to create a gradient of soil metal availability; covering ranges of both soil metal contents and of several soil parameters. Following exposure, Cd, Pb and Zn concentrations were determined both in total earthworm body and in three subcellular compartments: cytosolic, granular and debris fractions. Three distinct proxies of soil metal availability were investigated: CaCl2-extractable content dissolved content predicted by a semi-mechanistic model and free ion concentration predicted by a geochemical speciation model. Subcellular partitionings of Cd and Pb were modified along the gradient of metal exposure, while stable Zn partitioning reflected regulation processes. Cd subcellular distribution responded more strongly to increasing soil Cd concentration than the total internal content, when Pb subcellular distribution and total internal content were similarly affected. Free ion concentrations were better descriptors of Cd and Pb subcellular distribution than CaCl2 extractable and dissolved metal concentrations. However, free ion concentrations and soil total metal contents were equivalent descriptors of the subcellular partitioning of Cd and Pb because they were highly correlated. Considering lowly contaminated soils, our results raise the question of the added value of three proxies of metal availability compared to soil total metal content in the assessment of metal bioavailability to earthworm.

Is there a relationship between earthworm energy reserves and metal availability after exposure to field-contaminated soils?

Generic biomarkers are needed to assess environmental risks in metal polluted soils. We assessed the strength of the relationship between earthworm energy reserves and metal availability under conditions of cocktail of metals at low doses and large range of soil parameters. Aporrectodea caliginosa was exposed in laboratory to a panel of soils differing in Cd, Pb and Zn total and available (CaCl2 and EDTA-extractable) concentrations, and in soil texture, pH, CEC and organic-C. Glycogen, protein and lipid contents were recorded in exposed worms. Glycogen contents were not linked to the explaining variables considered. Variable selection identified CaCl2 extractable metals concentrations and soil texture as the main factors affecting protein and lipid contents. The results showed opposite effects of Pb and Zn, high inter-individual variability of biomarkers and weak relationships with easily extractable metals. Our results support the lack of genericity of energy reserves in earthworms exposed to field-contaminated soils.

Soil acidification increases metal extractability and bioavailability in old orchard soils of Northeast Jiaodong Peninsula in China

The bioavailability of Cu, Zn, Pb and Cd from field-aged orchard soils in a certified fruit plantation area of the Northeast Jiaodong Peninsula in China was assessed using bioassays with earthworms (Eisenia fetida) and chemical assays. Soil acidity increased with increasing fruit cultivation periods with a lowest pH of 4.34. Metals were enriched in topsoils after decades of horticultural cultivation, with highest concentrations of Cu (132 kg(-1)) and Zn (168 mg kg(-1)) in old apple orchards and Pb (73 mg kg(-1)) and Cd (0.57 mg kg(-1)) in vineyard soil. Earthworm tissue concentrations of Cu and Pb significantly correlated with 0.01 M CaCl2-extractable soil concentrations (R(2) = 0.70, p < 0.001 for Cu; R(2) = 0.58, p < 0.01 for Pb). Because of the increased bioavailability, regular monitoring of soil conditions in old orchards and vineyards is recommended, and soil metal guidelines need reevaluation to afford appropriate environmental protection under acidifying conditions.

Utilizing thin-film solid-phase extraction to assess the effect of organic carbon amendments on the bioavailability of DDT and dieldrin to earthworms

Improved approaches are needed to assess bioavailability of hydrophobic organic compounds in contaminated soils. Performance of thin-film solid-phase extraction (TF-SPE) using vials coated with ethylene vinyl acetate was compared to earthworm bioassay (Lumbricus terrestris). A DDT and dieldrin contaminated soil was amended with four organic carbon materials to assess the change in bioavailability. Addition of organic carbon significantly lowered bioavailability for all compounds except for 4,4'-DDT. Equilibrium concentrations of compounds in the polymer were correlated with uptake by earthworms after 48d exposure (R(2) = 0.97; p < 0.001), indicating TF-SPE provided an accurate uptake simulation. Bioavailability of residues in soil was compared with a spiked soil aged for 90d in laboratory. Dieldrin and DDX were respectively 18% and 11% less bioavailable in contaminated soil relative to spiked soil despite >40yr of aging. Results show that TF-SPE can be useful in examining potential risks associated with contaminated soils and to test effectiveness of remediation efforts.

Chemical measures of bioavailability/bioaccessibility of PAHs in soil: fundamentals to application

Risk assessment and remediation of contaminated land is inherently dependent on the contaminants present and their availability for interaction with soil biota. An ever-growing body of evidence suggests that current regulatory procedures over-estimate the 'true' fraction available to biota. Thus, a procedure that predicts the 'bioavailable fraction' would be useful for predicting 'actual' exposure limits and provide a more relevant basis for risk assessment. The aim of this paper is to address several important questions: "How should bioavailability be defined?" "What factors affect bioavailability measurement?" "To what extent have existing protocols measured bioavailability?" "What is actually measured by chemical techniques purported to determine bioavailability?" We offer two definitions (namely 'bioavailability' and 'bioaccessibility') and review commonly employed chemical extraction techniques to measure putative bioavailability. Relative advantages and disadvantages of the techniques are highlighted to elucidate underlying factors for the wide range of conclusions observed in the literature. Although the concept of bioavailability is implicit to contaminated land risk assessment and remediation, explicit reference to and use of adjustment factors is rare amongst regulatory bodies and remediators. Use of chemical determinants for bioavailability, applicable within current legislation and due consideration to inherent variability, are proposed and barriers to their implementation discussed.

Persistence and changes in bioavailability of dieldrin, DDE, and heptachlor epoxide in earthworms over 45 years

The finding of dieldrin (88 ng/g), DDE (52 ng/g), and heptachlor epoxide (19 ng/g) in earthworms from experimental plots after a single moderate application (9 kg/ha) 45 years earlier attests to the remarkable persistence of these compounds in soil and their continued uptake by soil organisms. Half-lives (with 95 % confidence intervals) in earthworms, estimated from exponential decay equations, were as follows: dieldrin 4.9 (4.3-5.7) years, DDE 5.3 (4.7-6.1) years, and heptachlor epoxide 4.3 (3.8-4.9) years. These half-lives were not significantly different from those estimated after 20 years. Concentration factors (dry weight earthworm tissue/dry weight soil) were initially high and decreased mainly during the first 11 years after application. By the end of the study, average concentration factors were 1.5 (dieldrin), 4.0 (DDE), and 1.8 (heptachlor epoxide), respectively.