Role of clay content in partitioning, uptake and toxicity of zinc in the earthworm Eisenia fetida

Assessment Toxicity of Soils from Areas with Mining Activity Through the Stability of the Lysosomal Membrane and Avoidance Behavior in the Earthworm Eisenia fetida

The aim of this study was to determine the effect of soils from areas with mining activity on the stability of the lysosomal membrane and avoidance behavior in the worm Eisenia fetida. Texture, organic material, conductivity and pH were determined in soils. The total concentrations of Cu, Zn, Pb, Ni, As and Hg were determined in tissues of E. fetida and in soils. Neutral red retention time (NRRT) was determined in hemocytes, and behavior with the avoidance test, in the earthworm. Cu (1563 ± 58 mg kg^-1) and Zn (135 ± 9 mg kg^-1) had the highest mean concentrations in the soils, while Hg (0.01 ± 0.001 mg kg^-1) had the lowest concentration in all the soils. The soil with the highest Cu concentration produced an avoidance of > 80%. Most of the soils produced a significant loss of the stability of the lysosomal membrane. The variables organic material and sand would facilitate habitat selection in E. fetida, In conclusion, the soils have chemical agents in bioavailable concentrations that provoke adverse cellular effects and evasion behavior. We propose the use of both response variables as early alerts in the evaluation of soils.

Update on the use of Pristina longiseta Ehrenberg, 1828 (Oligochaeta: Naididae) as a toxicity test organism

Ecotoxicological bioassays have been widely applied to evaluate the toxicity of substances in standardized test organisms. Nevertheless, the main challenge for researchers is the use of native species to express the effects of pollutants on aquatic biota. Thirty years ago, Smith and collaborators evaluate the possible use of Pristina longiseta (as Pristina leidyi) in acute toxicity test, developing some experiments using cadmium and vanadium as toxicants. The present work aimed to update the use of P. longiseta, in acute bioassays, presenting the occurrence and general characteristics of the species; adaptation of cultivation to tropical conditions; sensitivity tests using potassium chloride (KCl) and copper sulfate (CuSO₄) as reference substances standardized by OECD, USEPA, and ABNT; and acute exposure to zinc chloride (ZnCl₂). The results showed a successful use of this species as tropical test organism, which presented easy laboratory rearing and responded to the classical ecotoxicological index. The present study can increase the utilization of P. longiseta in bioassays for tropical regions and improve the evaluation of environmental impacts using a native species in ecotoxicological studies.

Single metal and metal mixture toxicity of five metals to Oppia nitens in five different Canadian soils

Metal mixture toxicity across soil types is a daunting challenge to risk assessment. Here, we evaluated metal mixture toxicity in Oppia nitens, using ten fixed metal mixture ratios in five Canadian soils that closely matched some of the EU PNEC reference soils. Soils were dosed with five metals (Cu, Zn, Pb, Co, Ni) as single metals (ten concentrations) and as mixtures (eight concentrations). Synchronized adult mites were exposed to metals, with survival and reproduction assessed after 28 days. We found out that (i) the differences among soils in mite sensitivity and single metals were not consistent when mites were exposed to metal mixtures, (ii) assuming concentration addition, the mixture interaction factor (MIF) showed that single metal low effect levels excessively underestimated low level metal mixture effects (iii) Zn emerged as a protective metal in most mixtures, and (iv) Soil properties such as CEC, independent of effects on metal speciation, explained more of the variation than measured metals. This study suggests that metal risk assessment should be done on a case by case basis. Further work is needed to ensure that by protecting soil-dwelling organisms from single metals, the risk from metal mixtures is appropriately protected for.

Heavy Metal Threats to Plants and Soil Life in Southern Africa: Present Knowledge and Consequences for Ecological Risk Assessment

In recent times there has been remarkable development in the field of soil ecotoxicology and risk assessment (RA) models. It is, however, debatable if these RA models are robust representatives for worldwide relevance. In order to investigate this, the current overview aims to address heavy metal threats to soil life in southern Africa by investigating present knowledge and consequences for RA using research in southern Africa as a case. To this end, the focus is on southern African soils, soil life and living conditions. To critically discuss these issues, we report on extensive research conducted in the southern African context and looked how comparable these findings are to RA models employed in the western world. This is done by providing an inventory of selected studies focused on the ecotoxicity of metals towards soil life. It is concluded that there is a dearth of information on southern African soil life, most of which are laboratory-based studies carried out by a handful of researchers. Future research incorporating the available information into a soil ecosystem assessment procedure is paramount. It is recommended that a starting point to tackle this might be the development of holistic sight-specific guidelines for ecological risk assessment at larger spatial scales (km²) which takes into cognizance landscapes, vegetation and faunal characteristics.

Study of zinc oxide nanoparticles and zinc chloride toxicity to annelid Enchytraeus crypticus in modified agar-based media

Acute toxicity of zinc oxide nanoparticle (ZnO-NP, mean particle size diameter of 10 nm) powder and water-soluble salt of zinc (ZnCl₂) to annelid Enchytraeus crypticus was tested using an agar-based nutrient-enriched medium with the addition of kaolin and humic acids (HA). Adults of the E. crypticus were cultivated in pure agar and in three types of modified exposure media containing different proportions of model soil constituents. Potworms were exposed to zinc in both forms (1-1000 mg kg^-1 of agar) for 96 h. In experiments with ZnCl₂, toxicity of zinc was the highest in pure agar followed by agar with HA and agar with kaolin and HA and the lowest toxicity was observed in agar with kaolin. The corresponding LC₅₀ values were 13.2, 28.8, 39.4, and 75.4 mg kg^-1 respectively. In contrast, zinc in the form of ZnO-NPs was most toxic in the presence of HA followed by pure agar, agar with kaolin, and kaolin with HA. In this case, LC₅₀ values were 15.8, 43.5, 111, and 122 mg kg^-1 respectively. Scanning electron microscopy revealed that the smallest agglomerates occurred in the presence of kaolin, where ZnO-NPs were sealed in a kaolin shell. This effect reduced the bioavailability and toxicity of the NPs. In contrast, larger agglomerates were observed in the presence of HA but a larger amount of zinc was dispersed in the volume of agar.

Target and non-target toxicity of botanical insecticide derived from Couroupita guianensis L. flower against generalist herbivore, Spodoptera litura Fab. and an earthworm, Eisenia foetida Savigny

Botanical insecticides may provide alternatives to synthetic insecticides for controlling Spodoptera litura (F.) and they are target specific, biodegradable, and harmless to mammals. Eight natural chemical compounds with larvicidal activity were identified from fraction F6 of C. guianensis flower extract. Probit analysis of 95% confidence level exposed an LC50 of 223ppm against S. litura third instar larvae. The growth and development of S. litura was affected in sub-lethal concentrations of fraction F6 (50, 100, 150 and 200ppm) compared to controls. Similarly nutritional indices values decreased significantly compared to controls. Fraction F6 also damaged the gut epithelial layer and brush border membrane (BBM). This study also resolved the effects of toxicity to non-target earthworm treated with fraction F6 and chemical pesticides (monotrophos and cypermethrin) and the results showed that fraction F6 had no harmful effect on E. fetida. Further, fraction F6 was eluted and sub fractions F6c (50ppm) showed high mortality against S. litura third instar larvae. Octacosane from fraction F6c was established and confirmed using IR spectrum and HPLC. The time of retention of fraction F6c was confirmed with the octacosane standard. Fraction F6 of C. guianensis extract caused dose-dependent mortality towards S. litura. Octacosane in fraction F6c was establish to be the prominent chemical compound associated with causing mortality but other compounds present in the fraction F6 were shown to be associated with changes in development of S. litura at low dosages. S. litura at low dosage. Therefore, these findings suggest that octacosane may be one of the major insecticidal compounds affecting S. litura survival.

Thresholds of arsenic toxicity to Eisenia fetida in field-collected agricultural soils exposed to copper mining activities in Chile

Several previous studies highlighted the importance of using field-collected soils-and not artificially-contaminated soils-for ecotoxicity tests. However, the use of field-collected soils presents several difficulties for interpretation of results, due to the presence of various contaminants and unavoidable differences in the physicochemical properties of the tested soils. The objective of this study was to estimate thresholds of metal toxicity in topsoils of 24 agricultural areas historically contaminated by mining activities in Chile. We performed standardized earthworm reproduction tests (OECD 222 and ISO 11268-2) with Eisenia fetida. Total soil concentrations of Cu, As, Zn, and Pb were in the ranges of 82-1295 mg kg(-1), 7-41 mg kg(-1), 86-345 mg kg(-1), and 25-97 mg kg(-1), respectively. In order to differentiate between the effects of different metals, we used regression analysis between soil metal concentrations and earthworm responses, as well as between metal concentrations in earthworm tissues and earthworm responses. Based on regression analysis, we concluded that As was a metal of prime concern for Eisenia fetida in soils affected by Cu mining activities, while Cu exhibited a secondary effect. In contrast, the effects of Zn and Pb were not significant. Soil electrical conductivity was another significant contributor to reproduction toxicity in the studied soils, forcing its integration in the interpretation of the results. By using soils with electrical conductivity ≤ 0.29 dS m(-1) (which corresponds to EC50 of salt toxicity to Eisenia fetida), it was possible to isolate the effect of soil salinity on earthworm reproduction. Despite the confounding effects of Cu, it was possible to determine EC10, EC25 and EC50 values for total soil As at 8 mg kg(-1), 14 mg kg(-1) and 22 mg kg(-1), respectively, for the response of the cocoon production. However, it was not possible to determine these threshold values for juvenile production. Likewise, we were able to determine EC10, EC25 and EC50 of earthworm tissue As of 38 mg kg(-1), 47 mg kg(-1), and 57 mg kg(-1), respectively, for the response of the cocoon production. Finally, we determined the no-observed effect concentration of tissue As in E. fetida of 24 mg kg(-1). Thus, earthworm reproduction test is applicable for assessment of metal toxicity in field-collected soils with low electrical conductivity, while it might have a limited applicability in soils with high electrical conductivity because the salinity-induced toxicity will hinder the interpretation of the results.

Effects of metals on earthworm life cycles: a review

Earthworms are abundant and ecologically very important organisms in the soil ecosystem. Impacts by pollutants on earthworm communities greatly influence the fertility of the terrestrial environment. In ecotoxicology, earthworms are good indicators of metal pollution. The observed median lethal concentrations (LC50) and the effective concentrations that cause 50% reduction of earthworm growth and reproduction (EC50) are referred to as toxicity concentrations or endpoints. In addition, the 'no observed effective concentration' (NOEC) is the estimation of the toxicity of metals on earthworms expressed as the highest concentration tested that does not show effects on growth and reproduction compared to controls. This article reviews the ecotoxicological parameters of LC50, EC50 and NOEC of a set of worms exposed to a number of metals in various tested media. In addition, this article reviews metal accumulation and the influences of soil characteristics on metal accumulation in earthworms. Morphological and behavioural responses are often used in earthworm toxicity studies. Therefore, earthworm responses due to metal toxicity are also discussed in this article.

The potentiation of zinc toxicity by soil moisture in a boreal forest ecosystem

Northern boreal forests often experience forest dieback as a result of metal ore mining and smelting. The common solution is to lime the soil, which increases pH, reducing metal toxicity and encouraging recovery. In certain situations, however, such as in Flin Flon, Manitoba, Canada, liming has yielded only moderate benefits, with some locations responding well to liming and other locations not at all. In an effort to increase the effectiveness of the ecorestoration strategy, the authors investigated if these differences in liming responsiveness were linked to differences in toxicity. Toxicity of metal-impacted Flin Flon soils on the oribatid mite Oppia nitens and the collembolan Folsomia candida was assessed, with a view toward identifying the metal of concern in the area. The effects of moisture content on metal sorption, uptake, and toxicity to the invertebrates were also investigated. Toxicity tests with the invertebrates were conducted using either Flin Flon soils or artificial soils with moisture content adjusted to 30%, 45%, 60%, or 75% of the maximum water-holding capacity of the soil samples. The Relative to Cd Toxicity Model identified Zn as the metal of concern in the area, and this was confirmed using validation tests with field contaminated soils. Furthermore, increasing the moisture content in soils increased the amount of mobile Zn available for uptake with the ion exchange resin. Survival and reproduction of both invertebrates were reduced under Zn exposure as moisture level increased. Thus, moisture-collecting landforms, which are often also associated with high Zn concentrations at Flin Flon, have, as a result, higher Zn toxicity to the soil ecosystem because of increases in soil moisture.

Assessing ecotoxicity and uptake of metals and metalloids in relation to two different earthworm species (Eiseina hortensis and Lumbricus terrestris)

Due to diffuse atmospheric fallouts of process particles enriched by metals and metalloids, polluted soils concern large areas at the global scale. Useful tools to assess ecotoxicity induced by these polluted soils are therefore needed. Earthworms are currently used as biotest, however the influence of specie and earthworm behaviour, soil characteristics are poorly highlighted. Our aim was therefore to assess the toxicity of various polluted soils with process particles enriches by metals and metalloids (Pb, Cd, Cu, Zn, As and Sb) collected from a lead recycling facility on two earthworm species belonging to different ecological types and thus likely to have contrasted behavioural responses (Eiseina hortensis and Lumbricus terrestris). The combination of behavioural factors measurements (cast production and biomass) and physico-chemical parameters such as metal absorption, bioaccumulation by earthworms and their localization in invertebrate tissues provided a valuable indication of pollutant bioavailability and ecotoxicity. Soil characteristics influenced ecotoxicity and metal uptake by earthworms, as well as their soil bioturbation.

Bioavailability pathways underlying zinc-induced avoidance behavior and reproduction toxicity in Lumbricus rubellus earthworms

We investigated possible bioavailability pathways underlying zinc-induced avoidance behavior and sublethal reproduction impairment in Lumbricus rubellus. Clay-loam (pH 7.3) and sandy soil (three pH values of 4.3-6.0) were amended with zinc sulfate at six soil concentrations of total Zn ranging from 0.1 to 36 mmol/kg dw. Estimated and measured concentrations of free and exchangeable Zn ranged 10(-4) to 7.1 mmol/l. Avoidance behavior responses were fast and could be directly predicted from the activity of free zinc ions without a modifying pH effect. The repellent effect is thus likely mediated by a direct action of Zn(2+) ions on epidermal chemosensitive receptors. Body zinc uptake, however, was determined by proton competition with free Zn(2+) sorption. Excess accumulation of body Zn was a good predictor of reproduction decline, which is indicative of internal zinc poisoning. The results indicated that zinc affects earthworms via both direct and indirect mechanisms of external and internal exposure.

Influence of clay content on bioavailability of copper in the earthworm Eisenia fetida

We investigated the effect of clay content on the bioavailability of copper to the earthworm Eisenia fetida, in the laboratory for 28 days using OECD artificial soil adjusted to 5%, 20% and 40% clay. Mortality, growth, cocoon production and internal copper concentrations were assessed in worms, and total, DTPA and CaCl(2) extractable copper in the substrates were also determined. The results showed that with increased clay content, there was significant reduction in internal Cu concentration of worms as well as toxicity of copper as shown by data for growth and mortality. However, internal copper concentrations of worms could not explain fully the observed toxicity in this study probably because of Cu regulation. Among the three extraction methods, DTPA extraction revealed the strongest relationship between partitioning and toxicity of Cu in this study. DTPA extract is thus a promising surrogate measure of bioavailability of Cu to earthworms. It is concluded that clay content has significant influence on the bioavailability of copper to earthworms and other similar species.