Rudo A. Verweij

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.

Polycyclic aromatic hydrocarbons in earthworms and isopods from contaminated forest soils

Abstract Individuals of the isopod species Porcellio scaber, Oniscus asellus and Philoscia muscorum and the earthworm species Lumbricus rubellus were collected at i0 sites with increasing distance from a blast furnace plant. PAH concentrations in the species decreased with increasing distance from the blast furnace plant. Each of the species contained a specific profile of PAHs. Animal concentrations correlated better with PAH levels in humus and fragmentation material than with levels in litter and mineral soil, which is consistent with the feeding behaviour of the animals. Biota-to-soil accumulation factors differed between the species and for the isopod species were negatively correlated with the octanol-water partition coefficient. This deviates from what is expected on the basis of the equilibrium partitioning theory. Possible non-equilibrium conditions are discussed. Cluster analysis of the PAH profiles observed in this study in conjunction with other terrestrial data from the literature, showed the presence of three main groups. One contained the profiles typical for atmospheric PAHs; the second cluster contained samples from earthworms, fragmentation, humus and mineral soil; the third contained litter and isopod profiles.

The influence of soil properties on the toxicity of molybdenum to three species of soil invertebrates

Mo toxicity to earthworms (Eisenia andrei), Collembola (Folsomia candida) and enchytraeids (Enchytraeus crypticus) was determined in 10 European soils and a standard artificial soil, freshly spiked with Na(2)MoO(4), after 28 days exposure. Mo affected survival only in three low pH sandy soils; in all other soils LC50 was >3200 mg Mo/kg dry soil. EC50 values for the reproduction toxicity of Mo were 129-2378 mg/kg for earthworms, 72->3396 mg/kg for Collembola, and 301->2820 mg/kg for enchytraeids. Variation in toxicity among soils could not be explained by differences in available (pore water, water and 0.01 M CaCl(2) extractable) Mo concentrations. Clay content best predicted the EC50 for Mo toxicity to earthworms, while toxicity of Mo for enchytraeids was best described by soil pH. For Collembola no relationships could be derived due to the absence of toxicity in most soils. Soil properties had a strong but species-specific effect on Mo toxicity to soil invertebrates.

Enchytraeus crypticus as model species in soil ecotoxicology

Enchytraeids are ecologically relevant soil organisms, due to their activity in decomposition and bioturbation in many soil types worldwide. The enchytraeid reproduction test (ERT) guidelines ISO 16387 and OECD 220 are exclusive to the genus Enchytraeus and recommend using the species E. albidus with a 6-week test period. The suggested alternative, E. crypticus has a shorter generation time which may enable the ERT to be twice as fast. To confirm the suitability of a 3-week test period for E. crypticus, the toxicity of five chemicals, with distinct properties and modes of action, was assessed in LUFA 2.2 soil. In all controls the validity criteria were met, as survival of E. crypticus was above 92% and more than 772 juveniles were produced. The good performance supports its appropriateness as model species. Reproduction was more sensitive than survival, with only cadmium and 3,5-dichloroaniline causing significant lethal effects in the tested concentration ranges. The effect concentration causing 50% reduction in the number of juveniles (EC50) was 35 mg kg(-1) for cadmium, <1.0 mg kg(-1) for carbendazim, 145 mg kg(-1) for phenanthrene, 275 mg kg(-1) for pentachloroaniline and 102 mg kg(-1) for 3,5-dichloroaniline. To evaluate the sensitivity of E. crypticus, the present results were compared to literature data for E. albidus. In conclusion, E. crypticus is a suitable model species in soil ecotoxicology, with advantages such as good control performance and speed, leading to a reliable and faster ERT.

Life cycle responses of the midge Chironomus riparius to compounds with different modes of action

Compounds with different modes of action may affect life cycles of biota differently. The aim of the present study was therefore to investigate the impact of four chemicals with different modes of action, including the essential metal copper, the nonessential metal cadmium, the organometal tributyltin, and the polycyclic aromatic compound phenanthrene, on chronic lethal and sublethal life-cycle effect parameters of the nonbiting midge Chironomus riparius, applying a 28-day sediment toxicity test. Tributyltin and cadmium delayed emergence significantly over a wide range of sublethal concentrations, while this range was narrow for copper and almost absent for phenanthrene. The chronic LC50/LOECEmT50 ratio, expressing these differences, amounted to 1.5, 3.5, 12.0, and 18.2 for respectively phenanthrene, copper, cadmium, and tributyltin. Thus the more specific the compounds mode of action, the higher the chronic LC50/LOECEmT50 ratio, as previously observed for acute-to-chronic ratios (ACRs). Comparison of our results with literature derived LC50/LOEC ratios showed a comparable trend and a lower variability compared to ACRs. We therefore conclude that the presently proposed chronic ratio is indicative for the specificity of a chemicals mode of action and that it is less variable than the ACR.

Gene Expression Analysis Reveals a Gene Set Discriminatory to Different Metals in Soil

Environmental pollution is a worldwide problem, and metals are the largest group of contaminants in soil. Microarray toxicogenomic studies with ecologically relevant organisms, such as springtails, supplement traditional ecotoxicological research but are presently rather descriptive. Classifier analysis, a more analytical application of the microarray technique, is able to predict biological classes of unknown samples. We used the uncorrelated shrunken centroid method to classify gene expression profiles of the springtail Folsomia candida exposed to soil spiked with six different metals (barium, cadmium, cobalt, chromium, lead, and zinc). We identified a gene set (classifier) of 188 genes that can discriminate between six different metals present in soil, which allowed us to predict the correct classes for samples of an independent test set with an accuracy of 83% (error rate = 0.17). This study shows further that in order to apply classifier analysis to actual contaminated field soil samples, more insight and information is needed on the transcriptional responses of soil organisms to different soil types (properties) and mixtures of contaminants.

Effect of long-term equilibration on the toxicity of molybdenum to soil organisms

To determine if long-term equilibration may alleviate molybdenum toxicity, earthworms, enchytraeids, collembolans and four plant species were exposed to three soils freshly spiked with Na(2)MoO(4).2H(2)O and equilibrated for 6 or 11 months in the field with free drainage. Total Mo concentrations in soil decreased by leaching, most (up to 98%) in sandy soil and less (54-62%) in silty and clayey soils. Changes in residual Mo toxicity with time were inconclusive in sandy soil. In the other two soils, toxicity of residual total Mo was significantly reduced after 11 months equilibration with a median 5.5-fold increase in ED50s. Mo fixation in soil, i.e. the decrease of soil solution Mo concentrations at equivalent residual total soil Mo, was maximally a factor of 2.1 only. This experiment shows natural attenuation of molybdate ecotoxicity under field conditions is related to leaching of excess Mo and other ions as well as to slow ageing reactions.

Effects of Benzo(a)pyrene on Food Assimilation and Growth Efficiency in Porcellio scaber (Isopoda)

Although the metabolic effects of benzo(a)pyrene have been investigated extensively in rodents, little is known about its effects in the terrestrial environment and nothing is known about its effects on soil invertebrates. In this study, the authors have chosen the woodlouse Porcellio scaber (Latr.) (Crustacea, Isopoda) as a representative from the soil invertebrate community. Experiments were designed to analyze the consequences of benzo(a)pyrene exposure for the energy metabolism. The partitioning of energy between respiration and scope for growth is considered as an ecologically relevant criterion for studying effects of contaminants in the environment. PAH might affect this partitioning by inducing biotransformation reactions that make demands on the assimilated energy.

Histidine-mediated xylem loading of zinc is a species-wide character in Noccaea caerulescens

Histidine plays a crucial role in nickel (Ni) translocation in Ni-hyperaccumulating plants. Here, we investigated its role in zinc (Zn) translocation in four accessions of the Zn hyperaccumulator, Noccaea caerulescens, using the related non-hyperaccumulator, Thlaspi arvense, as a reference. We compared the effects of exogenous histidine supply on Zn xylem loading, and of Zn-histidine complex formation on Zn uptake in energized tonoplast vesicles. The Zn distribution patterns over root tissues were also compared. Exogenous histidine supply enhanced Zn xylem loading in all the N. caerulescens accessions, but decreased it in T. arvense. Zn distribution patterns over root tissues were similar, apart from the accumulation in cortical and endodermal cells, which was much lower in N. caerulescens than in T. arvense. Zn uptake in energized tonoplast vesicles was inhibited significantly in N. caerulescens, but not affected significantly in T. arvense, when Zn was supplied in combination with histidine in a 1:2 molar ratio. Histidine-mediated Zn xylem loading seems to be a species-wide character in N. caerulescens. It may well have evolved as a component trait of the hyperaccumulation machinery for Zn, rather than for Ni.

Influence of earthworm activity on microbial communities related with the degradation of persistent pollutants

Earthworms may promote the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil, but the mechanism through which they exert such influence is still unknown. To determine if the stimulation of PAH degradation by earthworms is related to changes in microbial communities, a microcosm experiment was conducted consisting of columns with natural uncontaminated soil covered with PAH-contaminated dredge sediment. Columns without and with low and high Eisenia andrei densities were prepared. Organic matter and PAH content, microbial biomass, and dehydrogenase activity (DHA) were measured in soil and sediment over time. Biolog Ecoplate™ and polymerase chain reaction using denaturing gradient gel electrophoresis were used to evaluate changes in metabolic and structural diversity of the microbial community, respectively. Earthworm activity promoted PAH degradation in soil, which was significant for biphenyl, benzo[a]pyrene, and benzo[e]pyrene. Microbial biomass and DHA activity generally did not change over the experiment. Earthworm activity did change microbial community structure, but this did not affect its functioning in terms of carbon substrate consumption. Results suggest no relationship between changes in the microbial community by earthworm activity and increased PAH disappearance. The role of shifts in soil microbial community structure induced by earthworms in PAH removal needs further investigation.