Ecotoxicological Effects of Aflatoxins on Earthworms under Different Temperature and Moisture Conditions

Aflatoxin contamination remains one of the most important threats to food safety and human health. Aflatoxins are mainly found in soil, decaying plant material and food storage systems and are particularly abundant during drought stress. Regulations suggest the disposal of aflatoxin-contaminated crops by incorporation into the soil for natural degradation. However, the fate and consequences of aflatoxin in soil and on soil organisms providing essential ecological services remain unclear and could potentially pose a risk to soil health and productivity. The protection of soil biodiversity and ecosystem services are essential for the success of the declared United Nations Decade on Ecosystem Restoration. The focus of this study was to investigate the toxicological consequences of aflatoxins to earthworms’ survival, growth, reproduction and genotoxicity under different temperature and moisture conditions. Results indicated an insignificant effect of aflatoxin concentrations between 10 and 100 µg/kg on the survival, growth and reproduction but indicated a concentration-dependent increase in DNA damage at standard testing conditions. However, the interaction of the toxin with different environmental conditions, particularly low moisture, resulted in significantly reduced reproduction rates and increased DNA damage in earthworms.     

Population Genetic Structure of Earthworms (Lumbricus rubellus) in Soils Contaminated by Heavy Metals

The genetic structure of earthworm (Lumbricus rubellus) populations from plots (N=3) contaminated by sewage sludge (containing Cd, Cu, Pb, Zn) and reference plots (N=3) was compared. Earthworms (N=30–40 per plot) were collected during May 2000 and electrophoretic analyses were used to assess genetic variation at three polymorphic loci (GPI, LAP, PGM). Allele and genotype frequencies for GPI and PGM differed significantly between sludge and reference populations. Sludge populations were characterized by a reduced frequency of the most common genotype and allele at these loci, and the presence of alleles not found in the reference population. Allele and genotype frequencies did not differ significantly among individual plots within the sludge or the reference population. These results suggest that certain alleles and genotypes may be more sensitive to the effects of heavy metals. Multi-locus heterozygosity was significantly higher in the sludge population compared to the reference population; the proportion of individuals heterozygous at two or more loci was more than 15% higher in the sludge population. Results demonstrate that measures of population genetic structure in earthworms may represent useful biological indicators for the assessment of impacted terrestrial habitats.     

Fibrinolytic activity of earthworms extract (g-90) on lysis of fibrin clots originated from the venous blood of patients with malignant tumors

u-PA is secreted by the most malignant tumors. As a response to u-PA synthesis surrounding cells synthetize inhibitors of plasminogen activators for tissue protection. Plasminogen activators were found also in earthworm tissue. From the tissue homogenate of earthworm Eisenia foetida the glycolipoprotein mixture named G-90 was isolated. It contains two serine proteases (P I, P II) with fibrinolytic and anticoagulative activities. The fibrinolytic activity of G-90, P I and P II was tested in an in vitro euglobulinic test applied to fibrin clot from blood plasma of patients suffered from malignant tumors. G-90 and above-mentioned proteases applied in this study showed euglobulinic time proportionally with the concentrations of added substances. The influence of G-90 on the fibrinolysis rate does not depend only on its concentration, but depends too on histological type of tissue (organ) where the malignant tumors are located. Enzyme P I and P II do not show this activity.     

Estimating toxic damage to soil ecosystems from soil organic matter profiles

Concentrations of particulate and total organic matter were measured in upper soil profiles at 26 sites as a potential means to identify toxic damage to soil ecosystems. Because soil organic matter plays a role in cycling nutrients, aerating soil, retaining water, and maintaining tilth, a significant reduction in organic matter content in a soil profile is not just evidence of a change in ecosystem function, but of damage to that soil ecosystem. Reference sites were selected for comparison to contaminated sites, and additional sites were selected to illustrate how variables other than environmental contaminants might affect the soil organic matter profile. The survey was undertaken on the supposition that environmental contaminants and other stressors reduce the activity of earthworms and other macrofauna, inhibiting the incorporation of organic matter into the soil profile. The profiles of the unstressed soils showed a continuous decrease in organic matter content from the uppermost mineral soil layer (0–2.5cm) down to 15cm. Stressed soils showed an abrupt decrease in soil organic matter content below a depth of 2.5cm. The 2.5–5.0cm layer of stressed soils–such as found in a pine barren, an orchard, sites contaminated with zinc, and a site with compacted soil–had less than 4% total organic matter and less than 1% particulate organic matter. However, damaged soil ecosystems were best identified by comparison of their profiles to the profiles of closely matched reference soils, rather than by comparison to these absolute values. The presence or absence of earthworms offered a partial explanation of observed differences in soil organic matter profiles.     

Polycyclic Aromatic Hydrocarbon-Polluted Dredged Peat Sediments and Earthworms: A Mutual Interference

In lowland areas of the Netherlands, any peat sediments will gradually become enriched with anthropogenically derived Polycyclic Aromatic Hydrocarbons. Due to Dutch policy standards these (anaerobic) sediments are not allowed to be dredged and placed onto land. Under aerobic conditions, however, biodegradation of PAH is greatly enhanced. This degradation is further stimulated by colonisation of the sediments by earthworms. Laboratory experiments show that although earthworms do not avoid PAH-contaminated sediment, their burrowing-activity is reduced. Furthermore, these sediments have no significant ecotoxicological impacts on earthworms. Experimental introduction of earthworms into PAH-contaminated OECD-soil will result in a decrease in overall PAH content. In field surveys no significant differences in earthworm numbers between locations with fresh and old sediment could be found. It is concluded that dredging of PAH-contaminated sediment poses a very limited environmental threat, and that putting these sediments on land will improve PAH-biodegradation, partly through the colonisation by and activities of earthworms.     

Spidroin in carbopol-based gel promotes wound healing in earthworm's skin model

Spider silk's regenerative, biocompatible, and antimicrobial properties render it a promising biomaterial for wound healing promotion. Spidroin as the main protein component of spider silks was used in this study to evaluate the potential effects on wound healing via topical application of novel spidroin-containing carbopol 934 (CP934) gel. Spidroin was extracted, formulated into CP934 gel, and characterized both in vitro and in vivo. Spidroin gel was translucent and brownish-yellow in color. An optimum viscosity was obtained at 0.6% CP934 at neutral pH. Optimized spidroin gel (0.6% CP934) effectively inhibited the growth of clinical bacterial isolates of methicillin-sensitive Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (MRSA) and Escherichia coli at 440 μg/mL with MIC values of 0.98, 4.6, and 8.2 μg/mL, respectively. Optimized spidroin gel was evaluated for wound healing via topical application on wounds surgically induced in Allolobophora caliginosa earthworms used as a robust human skin model. After application for three consecutive days, dramatic reductions in wound closure and reepithelialization duration were observed macroscopically and via histological studies (light and electron microscopy) when compared with control. In conclusion, these results show that spidroin gel is a promising promoter for wound healing, and further studies would be directed toward investigating mechanisms underlying this effect.     

Soil pH effects on the comparative toxicity of dissolved zinc,non-nano and nano ZnO to the earthworm Eisenia fetida

To determine how soil properties influence nanoparticle (NP) fate, bioavailability and toxicity, this study compared the toxicity of nano zinc oxide (ZnO NPs), non-nano ZnO and ionic ZnCl₂ to the earthworm Eisenia fetida in a natural soil at three pH levels. NP characterisation indicated that reaction with the soil media greatly controls ZnO properties. Three main conclusions were drawn. First that Zn toxicity, especially for reproduction, was influenced by pH for all Zn forms. This can be linked to the influence of pH on Zn dissolution. Secondly, that ZnO fate, toxicity and bioaccumulation were similar (including relationships with pH) for both ZnO forms, indicating the absence of NP-specific effects. Finally, earthworm Zn concentrations were higher in worms exposed to ZnO compared to ZnCl₂, despite the greater toxicity of the ionic form. This observation suggests the importance of considering the relationship between uptake and toxicity in nanotoxicology studies.     

Effects of low levels of lead on growth and reproduction of the Asian earthworm Perionyx excavatus (Oligochaeta)

The effects of sublethal concentrations of lead nitrate on growth and reproduction of the Asian composting earthworm species Perionyx excavatus was studied experimentally by exposing worms in an organic substrate to lead nitrate-contaminated food over a period of 76 days. The results revealed that growth was affected negatively by the presence of lead while maturation rate and cocoon production was not affected. In agreement with other studies on Eisenia fetida, cocoon viability was affected negatively by lead, making this a sensitive toxicity endpoint. Lead accumulation was of the same order of magnitude as for other previously studied species.     

Effect of Cd or Pb Addition to Cu-Contaminated Soil on Tissue Cu Accumulation in the Earthworm,Dendrobaena veneta

Generally, soil heavy metal contamination consists of a mixture of heavy metals. Soil chemical properties and interaction with other pollutants in soil affect the external heavy metal bioavailability. Moreover, interaction with other pollutants accumulated in organisms may change the toxicity of each pollutant. Therefore, the hypotheses was tested that addition of Cd or Pb to Cu-contaminated soil would lead to an increase in tissue Cu accumulation in the earthworm,Dendrobaena veneta,caused by (i) induction of metallothionein by Cd, or (ii) an increase in Cu concentration in soil solution due to the exchange of adsorbed Cu for Pb. Tissue heavy metal concentrations were determined after exposure in contaminated soils for 3 or 21 days. Considerable amounts of Cu, Cd, and Pb were accumulated, indicating that these heavy metals were available for uptake byD. veneta.Both Cd and Pb, however, did not significantly affect tissue Cu accumulation.     

Uptake,Retention, and Excretion of Infectious Prions by Experimentally Exposed Earthworms

Prions are proteinaceous infectious agents that can be transmitted through various components of the environment, including soil particles. We found that earthworms exposed to prion-contaminated soil can bind, retain, and excrete prions, which remain highly infectious. Our results suggest that earthworms potentially contribute to prion disease spread in the environment.