C.A.M. van Gestel

Incorporation of the biomarker concept in ecotoxicology calls for a redefinition of terms.

Biomarkers have received a lot of attention but the biomarker concept has not yet been defined properly. As a consequence, various interpretations of the term ‘biomarker’ exist, some of which overlap with well-established ecotoxicological concepts. To allow incorporation of the biomarker concept within the framework of modern ecotoxicology, a clarification of terms is needed. In this paper, definitions are presented for the terms ‘biomarker’, ‘bioindicator’ and ‘ecological indicator’, which do not overlap and are linked to different levels of biological organization. The use of these concepts for ecological effects assessment is discussed.

Toxicity and bioaccumulation of chlorophenols in earthworms, in relation to bioavailability in soil.

The acute toxicity of five chlorophenols for two earthworm species was determined in two sandy soils differing in organic matter content and the results were compared with adsorption data. Adsorption increased with increasing organic matter content of the soils, but for tetra- and pentachlorophenol was also influenced by soil pH. Earthworm toxicity was significantly higher in the soil with a low level of organic matter. This difference disappeared when LC50 values were recalculated to concentrations in soil solution using adsorption data. Eisenia fetida andrei showed LC50 values lower than those of Lumbricus rubellus although bioaccumulation was generally higher in the latter species. Toxicity and bioaccumulation based on soil solution concentrations increased with increasing lipophilicity of the chlorophenols. The present results indicate that the toxicity and bioaccumulation and therefore the bioavailability of chlorophenols in soil to earthworms are dependent on the concentration in soil solution and can be predicted on the basis of adsorption data. Both the toxicity of and bioaccumulation data on chlorophenols in earthworms demonstrated surprisingly good agreement with those on chlorophenols in fish.

Development of a standardized reproduction toxicity test with the earthworm species Eisenia fetida andrei using copper, pentachlorophenol, and 2,4-dichloroaniline

This article describes a standardized test method for determining the effect of chemical substances on the reproduction of the earthworm Eisenia fetida andrei. It is based on the existing guidelines for acute toxicity testing with earthworms, and for reasons of standardization the same artificial soil substrate and earthworm species were chosen as prescribed by these guidelines. After being preconditioned for one week in untreated soil, earthworms are exposed to the chemical substances for 3 weeks. The number of cocoons produced is determined, and cocoons are incubated in untreated artificial soil for 5 weeks to assess hatchability. Results are presented from toxicity experiments with pentachlorophenol, copper, and 2,4-dichloroaniline. For these compounds no-effect levels (NEL) for cocoon production were 32, 60-120, and 56 mg.kg-1 dry soil, respectively. Hatching of cocoons was influenced by pentachlorophenol (NEL, 10 mg.kg-1), but not by copper and dichloroaniline. Following exposure, earthworms were incubated in clean soil again to study the possibility of recovery of cocoon production. For copper and dichloroaniline earthworms did recover cocoon production to a level as high as the control level or even higher; in case of pentachlorophenol, cocoon production was still reduced after 3 weeks in clean soil.

Bioavailability and ecological effects of cadmium on Folsomia candida (Willem) in an artificial soil substrate as influenced by pH and organic matter

The validity of the pore-water hypothesis was studied by determining the bioavailability and toxicity of cadmium to the collembolan species Folsomia candida, in artificial soils with different pH and different organic matter content. Cadmium solubility, cadmium accumulation by individuals and effects on survival, growth and population-increase were determined. Water soluble cadmium concentrations, at comparable total soil concentrations, increased with decreasing pH and decreasing organic matter content of the soil. No consistent pattern in accumulation of cadmium by Collembola was found for the different treatments. The variation in LC50 values and EC50 values for growth and population increase, increased when effects were expressed as soluble concentrations instead of total concentrations in the soil. When expressed as internal concentrations the variation decreased except for population increase at different pHs. It may, therefore, be concluded that the bioavailability of cadmium to F. candida is not predicted by the water soluble concentration and that collembolan sensitivity is not only determined by the internal cadmium concentration but also by differences in soil characteristics. This hampers a straight-forward prediction of metal toxicity using the pore-water hypothesis.

Comparison of sublethal and lethal criteria for nine different chemicals in standardized toxicity tests using the earthworm Eisenia andrei

In this study, the effects of nine different chemicals on the survival, growth, and reproduction of the earthworm species Eisenia andrei were determined using a recently developed method. Earthworms were exposed for 3 weeks to the test chemicals in an artificial soil substrate. Additional data on the acute toxicity of these chemicals were derived from the literature. For some chemicals, cocoon production was the most sensitive parameter (cadmium, chromium, paraquat, fentin, benomyl, phenmedipham), while for others cocoon hatchability was most sensitive (pentachlorophenol, parathion, carbendazim). In the case of parathion, growth of the worms seemed to be even more sensitive than reproduction. As an overall parameter for the effect on earthworm reproduction, the total number of juveniles produced per worm appeared to be a useful parameter. Differences between (acute) LC50 values and the lowest NOEC value for effects on growth and reproduction were different for each chemical. Difference was greatest for cadmium (a factor of greater than 100) and smallest for fentin, benomyl, and pentachlorophenol (a factor of 5-6).

Accumulation and elimination of cadmium, chromium and zinc and effects on growth and reproduction in Eisenia andrei (Oligochaeta, Annelida)

Abstract Accumulation and elimination of cadmium, chromium and zinc and effects on the growth and reproduction of the earthworm Eisenia andrei were determined in an artificial soil. Cadmium at the lowest soil concentration tested (10 mg/kg) significantly reduced cocoon production, whereas cadmium concentrations in the earthworms at the end of the 3-week exposure period were significantly increased in a dose-related manner at all concentrations tested. Reproduction was completely recovered at the end of a 3-week recovery period in untreated soil, although cadmium concentrations in the earthworms were still significantly elevated. Apparently, the remaining cadmium residues in the worms were strongly bound, and therefore no longer exerted a toxic effect on the reproduction of earthworms. Chromium was significantly accumulated and earthworm reproduction significantly reduced at soil concentrations of 100 mg/kg and higher. Chromium was completely eliminated and reproduction no longer affected at the end of a 3-week recovery period. Zinc significantly reduced reproduction at soil concentrations of 560 and 1000 mg/kg, and induced the production of malformed cocoons. Earthworms were able to regulate their body content of zinc; only at 1000 mg/kg dry soil were zinc concentrations significantly increased. At the end of a 3-week recovery period zinc concentrations in the earthworms had returned to the control level, and reproduction was completely recovered.

Enrichment of polycyclic aromatic hydrocarbons in forest soils near a blast furnace plant

Four different layers of soil were sampled at ten sites at increasing distances from a blast furnace plant. PAH 7 concentrations decreased exponentially from moderately contaminated to background values. For each compound it was possible to distinguish between the source-related part, decreasing with increasing distance from the plant, and the background contribution. The relative contribution of PAHs differed between the source and the background profiles. PAH concentrations were found to be elevated upto a distance of 2 km from the boundary of the plant. The different layers of soil revealed a relative enrichment of PAHs with ageing of organic matter. This effect, which increased with the molecular weight of the compound, was used to estimate the half-life of PAHs in forest soil. Estimated DT 50s ranged from 2 to 4 months for fluorene upto 1.9 to 3.4 years for benzo[b]fluoranthene.

The influence of soil characteristics on the toxicity of four chemicals to the earthworm Eisenia fetida andrei (Oligochaeta)

SummaryThe acute toxicity of Cd (chloride), chloroacetamide, 3,4-dichloroaniline and pentachlorophenol to the earthworm Eisenia fetida andrei was determined using the OECD (1984) artificial soil and contact testing procedures. To investigate the influence of two soil characteristics (pH and organic-matter content), the toxicity of the chemicals was also determined in two natural sandy soils. It is concluded that the filter-paper contact test cannot be recommended to predict earthworm toxicity of these chemicals in soil. Toxicity in soil was influenced by both pH and organic-matter content. Differences between LC50 values in the high-organic-matter artificial soil and in an acid, low-organic-matter sandy soil were, however, not greater than a factor of 3–4. The results of this study therefore support the use of a well-defined artificial soil substrate for standardized earthworm toxicity tests.

An approach to quantitative structure-activity relationships (QSARs) in earthworm toxicity studies.

Abstract Two-wk LC 50 values for earthworms in soil were determined for a homologous series of seven organic chemicals, i.e., 1,2,3-trichlorobenzene, 2,4-dichloroaniline and five chlorophenols. The toxicity tests were conducted with two species, i.e., Eisenia andrei and Lumbricus rubellus , and four different soil types, i.e., two sandy soils, a peaty soil, and an artificial soil. The LC 50 values were recalculated towards molar concentrations in pore water using data from soil adsorption experiments. Significant relationships were obtained between LC 50 values (in μmol/l pore water) and the octanol/water partition coefficient (log P oct ) of the compounds. The described approach will be useful for developing QSARs for the toxicity of chemicals in soil for earthworms.

Comparison of the toxicity of zinc for the springtail Folsomia candida in artificially contaminated and polluted field soils

To evaluate the influence of soil characteristics and chemical application form on the ecotoxicity of zinc, the toxicity of contaminated soil samples from the vicinity of a zinc smelter was compared with the effects of ZnCl2 added to two uncontaminated natural soils. Tests were performed with the springtail Folsomia candida (Willem). In the artificially contaminated soils, ZnCl2 had a strong effect on reproduction, whereas the effects on growth were not conclusive. In the polluted field soil however, no relationship was observed between zinc concentrations and growth or reproduction. Chemical analysis of the soils used showed that water soluble concentrations were higher in the artificially contaminated soils than in the polluted field soil. However, differences in water soluble zinc concentrations could not fully explain the differences in effects among the soils. It is concluded that because of the influence of soil type and chemical form of zinc on bioavailability and toxicity, artificially contaminated soils should be used with caution in ecotoxicological risk assessment. It is recommended to include soil pore water analysis in future research to improve the interpretation and application of results obtained in artificially contaminated soils.