The effect of sublethal lead exposure on the ultrastructure and on the distribution of acid phosphatase activity in chloragocytes of earthworms (Annelida, Oligochaeta)

Morphophysiological and Histopathological Effects of Ammonium Sulfate Fertilizer on Aporrectodea trapezoides (Dugès, 1828) Earthworm

The present study used the adult earthworm Aporrectodea trapezoides as a bioindicator species to look into the possible dangers of ammonium sulfate (AS) fertilizer. Two complementary toxicity tests were conducted to determine the LC50values, growth rate inhibition, morphological alterations, and histopathological texture of worms. The lethality test included four increasing concentrations of AS fertilizer (ranging from 2500 to 7500 mg/kg of dry soil weight (d.w.)), while sub-lethal concentrations were based on 10%, 30%, 40%, and 50% of the 14-day median lethal concentration (LC50), with a control group included for both tests. The LC(50) values for AS fertilizer were significantly higher at 7 days (4831.13 mg/kg d.w.) than at 14 days (2698.67 mg/kg d.w.) of exposure. Notably, earthworms exhibited significant growth rate inhibition under exposure to various concentrations and time durations (14/28 exposure days). Morphological alterations such as clitellar swelling, bloody lesions, whole body coiling and constriction, body strangulation, and fragmentation were accentuated steadily, with higher concentrations. Histopathological manifestations included severe injuries to the circular and longitudinal muscular layers, vacuolation, muscle layer atrophy, degradation of the chloragogenous tissue in the intestine, collapsed digestive epithelium of the pharynx with weak reserve inclusion, and fibrosis of blood vessels. These effects were primarily influenced by increasing concentrations of fertilizer and time exposure. The study highlights the strong relationship between concentration and exposure time responses and underscores the potential of A. trapezoides earthworms as valuable biological control agents against acidic ammonium sulfate fertilizer. Importantly, this research contributes to the use of such biomarkers in evaluating soil toxicity and the biological control of environmental risk assessment associated with chemical fertilizers.

Toxic mechanism on phenanthrene-triggered cell apoptosis, genotoxicity, immunotoxicity and activity changes of immunity protein in Eisenia fetida: Combined analysis at cellular and molecular levels

Phenanthrene (PHE) is a harmful organic contaminant and exists extensively in the soil environment. The accumulation of PHE would potentially threaten soil invertebrates, including earthworms, and the toxicity is also high. Currently, the possible mechanisms underlying apoptotic pathways induced by PHE and its immunotoxicity and genotoxicity in earthworms remain unclear. Thus, Eisenia fetida coelomocytes and immunity protein lysozyme (LYZ) were chosen as targeted receptors to reveal the apoptotic pathways, genotoxicity, and immunotoxicity triggered by PHE and its binding mechanism with LYZ, using cellular, biochemical, and molecular methods. Results indicated that PHE exposure can cause cell membrane damage, increase cell membrane permeability, and ultimately trigger mitochondria-mediated apoptosis. Increased 8-hydroxy-2-deoxyguanosine (8-OHdG) levels indicated PHE had triggered DNA oxidative damage in cells after PHE exposure. Occurrence of detrimental effects on the immune system in E. fetida coelomocytes due to decreased phagocytic efficacy and destroyed the lysosomal membrane. The LYZ activity in coelomocytes after PHE exposure was consistent with the molecular results, in which the LYZ activity was inhibited. After PHE binding, the protein structure (secondary structure and protein skeleton) and protein environment (the micro-environment of aromatic amino acids) of LYZ were destroyed, forming a larger particle size of the PHE-LYZ complex, and causing a significant sensitization effect on LYZ fluorescence. Molecular simulation indicated the key residues Glu 35, Asp 52, and Trp 62 for protein function located in the binding pocket, suggesting PHE preferentially binds to the active center of LYZ. Additionally, the primary driving forces for the binding interaction between PHE and LYZ molecule are hydrophobicity forces and hydrogen bonds. Taken together, PHE exposure can induce apoptosis by mitochondria-mediated pathway, destroy the normal immune system, and trigger DNA oxidative damage in earthworms. Besides, this study provides a comprehensive evaluation of phenanthrene toxicity to earthworms on molecular and cellular level.

Toxicological effect of Parthenium hysterophorus and milk processing industry sludge on earthworms, Eisenia fetida

Production of large quantities of organic waste all over the world poses major environmental and disposal problems. The present study was conducted to explore the deleterious effects of Parthenium hysterophorus and milk processing industry sludge on the health of earthworm, Eisenia fetida. Earthworms were allowed to grow in the mixture of cow dung:Parthenium hysterophorus (75:25) and cow dung:milk processing industry sludge (60:40) for 60 days. The biochemical markers viz. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and malondialdehyde (MDA) levels and histological changes in earthworm's intestine were assessed after 15, 30, 45, and 60 days of exposure. The results revealed increased MDA level, while SOD, CAT, and GPx activities showed variation in both treatments. Furthermore, histopathological changes revealed damage in the intestinal tissue in both treatments during all intervals. More severe effects were registered in P. hysterophorus treatment. Obtained results may contribute to the understanding of P. hysterophorus and milk processing industry sludge induced toxic effects on earthworms and to identify defense mechanism of Eisenia fetida.

Shift in phagocytosis, lysosomal stability, lysozyme activity, apoptosis and cell cycle profile in the coelomocytes of earthworm of polluted soil near a tannery field of India

Calcutta Leather Complex of the state of West Bengal, India has been designated as an industrially active zone with around 400 active tannery units. This area spanning 4.5 km² is surrounded by human habitation. The soil of this region is contaminated with metal pollutants and exhibited an alteration in selected physicochemical parameters, namely cation exchange capacity, moisture content, pH, total nitrogen, total organic carbon and water holding capacity. Metaphire posthuma, a common variety of endogeic earthworm inhabiting this region is thus continuously exposed to these toxic metals. Coelomocytes, the chief immune effector cells of earthworm presented a shift in phagocytosis, lysosomal membrane stability, lysozyme and phosphatase activity, physiological apoptosis and cell cycle profile of M. posthuma sampled from the soil of tannery industry. Presence of high concentration of toxic metals and change in the physicochemical characteristics of soil led to a state of cellular stress and immunocompromisation in M. posthuma, a common inhabitant of soil of this region. Experimental endpoints bear ecotoxicological significance as biomarkers of physiological stress in earthworm for monitoring the health of soil around this tannery industrial zone.

Unravelling the ZnO-NPs mechanistic pathway: Cellular changes and altered morphology in the gastrointestinal tract of the earthworm Eisenia andrei

A major uptake route of nanoparticles (NPs) occurs via the gastrointestinal (GI) tract. When GI tract cells are exposed, NPs cytotoxic effects are observed that subsequently adversely affect the GI tract morphology and have consequences for the whole organism. The aim of this study was to understand the mechanism of effects caused by ZnO-NPs compared to Zn ions on the earthworm Eisenia andrei. The following aspects of individually exposed earthworms were investigated: 1) qualitative structural alterations in the gut epithelium and chloragogen cells of the GI tract, 2) quantitative changes within chloragogen tissues after 48 h of exposure (using morphometric analysis), and 3) the ADP/ATP ratio in homogenized tissue of the whole organism after 21 days of exposure to contaminated soil (contamination phase) followed by 14 days of elimination in clean soil (decontamination phase) to identify possible recovery. Both ZnO-NPs and Zn ions adversely affect the gut epithelium and chloragogen tissue of earthworms after 48 h of exposure to contaminated soil. Morphometric measurements revealed that the proportions of debris vesicles in the chloragocytes were significantly lower in worms exposed to ZnO-NPs than in worms exposed to Zn ions. Moreover, numerous spherite granules were observed in the chloragocytes of ionic Zn-treated worms, but not the ZnO-NPs-treated worms, suggesting differential regulation of these Zn forms. The Zn cytotoxic effect was not reflected in ADP/ATP ratio measurements. Our study provides new insights into nano-specific effects that are distinctive from ion regulation inside the GI tract and furthers our understanding of the relationship between effects at the cellular and whole-body levels.

Immunotoxicity of copper nanoparticle and copper sulfate in a common Indian earthworm

Copper oxide nanoparticles and copper sulfate are established contaminants of water and soil. Metaphire posthuma is a common variety of earthworm distributed in moist soil of Indian subcontinent. Comparative toxicity of copper nanoparticles and copper sulfate were investigated with reference to selected immune associated parameters of earthworm. Total count, phagocytic response, generation of cytotoxic molecules (superoxide anion, nitric oxide), activities of enzymes like phenoloxidase, superoxide dismutase, catalase, acid phosphatase, alkaline phosphatase and total protein of coelomocytes were estimated under the exposures of 100, 500, 1000mg of copper oxide nanoparticles and copper sulfate per kg of soil for 7 and 14 d. A significant decrease in the total coelomocyte count were recorded with maximum depletion as 15.45 ± 2.2 and 12.5 ± 2 × 10⁴ cells/ml under the treatment of 1000mg/kg of copper nanoparticles and copper sulfate for 14 d respectively. A significant decrease in generation of nitric oxide and activity of phenoloxidase were recorded upon exposure of both toxins for 7 and 14 d indicating possible decline in cytotoxic status of the organism. A maximum inhibition of superoxide dismutase activity was recorded as 0.083 ± 0.0039 and 0.055 ± 0.0057 unit/mg protein/minute against 1000mg/kg of copper nanoparticles and copper sulfate treatment for 14 d respectively. Activities of catalase and alkaline phosphatase were inhibited by all experimental concentrations of both toxins in the coelomocytes of earthworm. These toxins were recorded to be modifiers of the major immune associated parameters of M. posthuma. Unrestricted contamination of soil by sulfate and oxide nanoparticles of copper may lead to an undesirable shift in the innate immunological status of earthworm leading to a condition of immune compromisation and shrinkage in population density of this species in its natural habitat. This article is the first time report of immunological toxicity of nanoparticles and sulfate salt of copper in M.posthuma inhabiting the soil of India, an agriculture based country.

Lethal and sub-lethal effects of five pesticides used in rice farming on the earthworm Eisenia fetida

The toxicity of five pesticides typically used in rice farming (trichlorfon, dimethoate, carbendazim, tebuconazole and prochloraz) was evaluated on different lethal and sub-lethal endpoints of the earthworm Eisenia fetida. The evaluated endpoints included: avoidance behaviour after an exposure period of 2 days; and mortality, weight loss, enzymatic activities (cholinesterase, lactate dehydrogenase and alkaline phosphatase) and histopathological effects after an exposure period of 14 days. Carbendazim was found to be highly toxic to E. fetida (LC50=2mg/kg d.w.), significantly reducing earthworm weight and showing an avoidance response at soil concentrations that are close to those predicted in rice-fields and in surrounding ecosystems. The insecticide dimethoate showed a moderate acute toxicity (LC50=28mg/kg d.w.), whereas the rest of tested pesticides showed low toxicity potential (LC50 values above 100mg/kg d.w.). For these pesticides, however, weight loss was identified as a sensitive endpoint, with NOEC values approximately 2 times or lower than the calculated LC10 values. The investigated effects on the enzymatic activities of E. fetida and the observed histopathological alterations (longitudinal and circular muscle lesions, edematous tissues, endothelial degeneration and necrosis) proved to be sensitive biomarkers to monitor pesticide contamination and are proposed as alternative measures to evaluate pesticide risks on agro-ecosystems.

Indication of metal homeostasis disturbance in earthworm Eisenia fetida after exposure to semi-solid depot sludge

Treated sewage sludge is commonly used in agriculture as fertilizer. It is, therefore, necessary to determine possible detrimental influences of sludge application on soil contamination and accumulation of contaminants in tissues of terrestrial animals, which in the long run could also have undesirable effects on humans. With that aim, the study was performed using earthworm Eisenia fetida as test organism and semi-solid depot sludge from a wastewater treatment plant as exposure media. The concentrations of 26 metals/metalloids were determined in depot sludge, and their bioaccumulation was estimated in whole tissue of E. fetida, and for the first time in the soluble tissue fraction, which represents metal fraction available for metabolic requirements and toxic effects. Obtained results have revealed acceptable levels of several elements (Cd, Cr, Cu, Ni, Pb, Zn) in depot sludge, when compared to currently valid regulations, and only moderate accumulation of some elements (e.g. As, Ba, Cd, Co, Fe, Tl, V, and Zn) in earthworms, as a consequence of exposure to depot sludge. However, a concentration increase after exposure to depot sludge was observed in E. fetida for several elements (Cd, Mo, and Zn), which were present in lower concentrations in the exposure mixtures than in soil. Contrary, a concentration decrease was observed for Cs, Mn, and Rb, although they were present in higher concentrations in depot sludge than in soil. It was an indication of disturbance in metal homeostasis in earthworms, possibly caused by exposure to complex mixture of contaminants present in depot sludge. The cumulative effect of exposure to a number of various contaminants (inorganic, organic, microbiological and pharmaceutical), even if each of them was not present in very high concentrations, could have caused distress in earthworms exposed to depot sludge.

Effects of PAHs and dioxins on the earthworm Eisenia andrei: a multivariate approach for biomarker interpretation

In this study, a battery of biomarkers was utilised to evaluate the stress syndrome induced in the earthworm Eisenia andrei by exposure to environmentally realistic concentrations of benzo[a]pyrene (B[a]P) and 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD) in OECD soil. The set of tests was then employed to assess the toxicity of field soils contaminated with organic xenobiotic compounds (such as PAHs, dioxins and PCBs). The results highlighted an impairment of immune and metabolic functions and genotoxic damage in worms exposed also to lower bioavailable concentrations of toxic chemicals. Multivariate analysis of biomarker data showed that all different contaminated soils had a detrimental effect on the earthworms. A separation between temporal and concentration factors was also evident for B[a]P and TCDD treatments; and field contaminated soils were further differentiated reflecting a diverse contamination. Multivariate analysis also demonstrated that lysosomal membrane stability can be considered a prognostic indicator for worm health status.

Vermiremoval of heavy metal in sewage sludge by utilising Lumbricus rubellus

Experiments were conducted to remove heavy metals (Cr, Cd, Pb, Cu and Zn) from urban sewage sludge (SS) amended with spent mushroom compost (SMC) using worms, Lumbricus rubellus, for 105 days, after 21 days of pre-composting. Five combinations of SS/SMC treatments were prepared in triplicate along with a control for each treatment in microcosms. Analysis of the earthworms' multiplication and growth and laboratory analysis were conducted during the tenth and fifteenth week of vermicomposting. Our result showed that the final biomass of earthworms (mg) and final number of earthworms showed significant differences between treatments i.e. F=554.70, P=0.00 and F=729.10, P=0.00 respectively. The heavy metals Cr, Cd and Pb contained in vermicompost were lower than initial concentrations, with 90-98.7 percent removal on week ten. However, concentrations of Cu and Zn, that are considered as micronutrients, were higher than initial concentrations, but they were 10-200-fold lower than the EU and USA biosolid compost limits and Malaysian Recommended Site Screening Levels for Contaminated Land (SSLs). An increment of heavy metals were recorded in vermicompost for all treatments on week fifteen compared to week ten, while concentration of heavy metals in earthworms' tissue were lower compared to vermicompost. Hence, it is suggested that earthworms begin to discharge heavy metals into their surroundings and it was evident that the earthworms' heavy metals excretion period was within the interval of ten to fifteen weeks.

Dynamic bioavailability of copper in soil estimated by uptake and elimination kinetics in the springtail Folsomia candida

This study aimed to assess the bioavailability of copper in soil, by measuring its uptake kinetics into a representative soil invertebrate, the collembolan Folsomia candida. The animals were exposed to 25 or 100 μg Cu g(-1) dry LUFA 2.2 soil at nominal pH(CaCl2) 4.5, 5.5, or 6.5 during 14 days after which they were transferred to clean soil for 14 days elimination. Uptake and elimination rate constants were calculated based on total and extractable soil concentrations and porewater concentrations using one-compartment first-order kinetics modelling. Copper was present in the animals at a basal physiological level of 40-90 μg g(-1)dry weight, on top of this uptake and elimination kinetics were observed. Uptake rates constants varied between 0.02 and 0.17 g(soil) g(animal)(-1) day(-1), being higher at lower exposure level, but did not differ significantly between different soil pH levels. Elimination rate constants ranged between 0.04 and 0.20 day(-1) and were negligible (k(2) < 0.001 day(-1)) at pH 4.5 and 6.5. Multiple linear regressions showed that the pH effect on copper uptake was only significant when taking into account cation exchange capacity, or calcium and dissolved organic carbon levels in the pore water. Copper concentrations in the animals however, never were higher than 185 μg g(-1) dry weight, independent of exposure level and pH, suggesting homeostatic regulation. These results show that the chemical composition of the pore water does affect bioavailability of copper in soil, but that copper uptake in collembolans is dominated by homeostatic regulation rather than by soil properties like pH.

Cold-stress induced formation of calcium and phosphorous rich chloragocyte granules (chloragosomes) in the earthworm Eisenia fetida

The cytochemical and functional characteristics of chloragocytes of both 'control' and cold-stressed Eisenia fetida were examined. Flow cytometry revealed the heterogeneity of chloragocytes: the first group was characterized by low, the second one by high acid phosphatase (AcP) content. In 'control' animals the former, in cold-stressed ones the latter type were the dominant form. The elevated AcP-activity correlated with the accumulation of autophagic vacuoles (AVs) in chloragocytes. Both AVs and all small chloragosomes showed high AcP activity, while most of the large chloragosomes did not display any. Most 'control' granules (0.75-1.25 μm) contained high amounts of Ca and P, with less and variable quantities of S, Cl, K, Fe and Zn. Small chloragosomes with low Ca and P concentrations were seldom found. In cold-stressed animals the number of small granules (0.25-0.75 μm) increased up to 40% of total population. Their Ca and P contents were significantly lower; S and Fe concentrations were higher than those of large chloragosomes (1.0-1.5 μm). Our results prove that the formation and elemental composition of chloragosomes can be influenced by environmental stressors and suggest that the mature chloragosomes are tertiary lysosomes and their formation is coupled to autophagocytosis.

Histopathological changes in the earthworm Eisenia andrei associated with the exposure to metals and radionuclides

Earthworms were exposed for 56 d to a contaminated soil, from an abandoned uranium mine, and to the natural reference soil LUFA 2.2. Histological changes in earthworm's body wall (epidermis, circular and longitudinal muscles) and gastrointestinal tract (chloragogenous tissue and intestinal epithelium) were assessed, after 0, 14 and 56 d of exposure. Results have shown alterations in all the studied tissues after 14 d of exposure (except for the intestinal epithelium), yet more severe effects were registered after 56 d of exposure. Herein we report histopathological alterations as a good biomarker for the evaluation of soil quality. We also demonstrate that morphological changes in the body wall and gastrointestinal tract, are important endpoints that could be added to earthworm's standardized tests, for the evaluation of soil toxicity, as part of the risk assessment of contaminated areas.

Effects of dioxin exposure in Eisenia andrei: integration of biomarker data by an Expert System to rank the development of pollutant-induced stress syndrome in earthworms

A battery of biomarkers has recently been developed in the earthworm Eisenia andrei. In this study, different biomarkers (i.e. Ca²⁺-ATPase activity, lysosomal membrane stability-LMS, lysosomal lipofuscin and neutral lipid content) were utilized to evaluate the alterations in the physiological status of animals, induced by exposure for 3d to different sublethal concentrations of TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) (1.5 × 10⁻³, 1.5 × 10⁻², 1.5×10⁻¹ ng mL⁻¹) utilizing the paper contact toxicity test. Lysosome/cytoplasm volume ratio and DNA damage were also evaluated as a biomarker at the tissue level and as a biomarker of genotoxicity, respectively. Moreover, the NR retention time assay conditions were optimized for the determination of in vivo LMS in earthworm coelomocytes. The results demonstrate that LMS and Ca²⁺-ATPase activity were early warning biomarkers able to detect the effects of minimal amounts of TCDD and that biomarkers evaluated at the tissue level are important for following the evolution of the stress syndrome in earthworms. To evaluate the health status of the animals, an Earthworm Expert System (EES) for biomarker data integration and interpretation was developed. The EES proved to be a suitable tool able to rank, objectively, the different levels of the stress syndrome in E. andrei induced by the different concentrations of TCDD.

Pollutant-induced alterations of granulocyte morphology in the earthworm Eisenia foetida

Earthworms are considered convenient indicators of land use and soil fertility. Recently the use of biomarkers in earthworms has been increasingly investigated. The aim of this work was to study possible pollutant-induced morphometric alterations in Eisenia foetida granulocytes in view of future applications as a sensitive, simple, and quick biomarker for soil monitoring and assessment applications. Results showed consistent enlargement of earthworm granulocytes induced by exposure to either copper sulfate or methiocarb. The increase of cellular size was time-dependent and was about 100% after 14 days of exposure for both treatments. In order to verify the applicability of morphometric granulocyte alteration, a battery of standardized biomarkers such as lysosomal membrane stability, metallothionein induction, or acetylcholinesterase (AChE) inhibition were also determined. We recommend the use of morphometric alterations of granulocytes as a suitable biomarker of pollutant effect to be included in a multibiomarker strategy including responses at different levels of biological organization.

Cd/Zn exposure interactions on metallothionein response in Eisenia fetida (Annelida, Oligochaeta)

We studied metallothionein (MT) response in the manure worm Eisenia fetida after exposures to cadmium (Cd), zinc (Zn) or cadmium and zinc spiked media. MT was studied both at the protein level by Dot Immunobinding Assay, (DIA) and at the expression level by Northern blotting. Cd was highly accumulated by worms whereas Zn body concentration was regulated. In addition, Zn would limit Cd accumulation in worms exposed to low Cd concentrations (1 and 8 mg Cd kg(-1) of dry soil). Exposure to a mixture of Cd and Zn at high concentrations increased cytosolic MT levels. This increase would allow worms to regulate body Zn concentrations and also to limit Cd toxicity. Cd exposures increased gene expression of Cd-binding MT isoform (MT 2A) whereas Zn did not. However, when both metals were at high concentrations in the exposure medium, this expression was further increased. Several hypotheses are proposed to explain the results and the best approach to estimate metal exposure of this earthworm species is given. Further experiments have now to be performed to evaluate the usefulness of these MT responses for field contaminated soils toxicity assessment using this earthworm species.

A review of studies performed to assess metal uptake by earthworms

Earthworms perform a number of essential functions in soil; the impacts of metals on earthworms are often investigated. In this review we consider the range of earthworm species, types of soil and forms of metal for which metal uptake and accumulation have been studied, the design of these experiments and the quantitative relationships that have been derived to predict earthworm metal body burden. We conclude that there is a need for more studies on earthworm species other than Eisenia fetida in order to apply the large existing database on this earthworm to other, soil dwelling species. To aid comparisons between studies agreement is needed on standard protocols that define exposure and depuration periods and the parameters, such as soil solution composition, soil chemical and physical properties to be measured. It is recommended that more field or terrestrial model ecosystem studies using real contaminated soil rather than metal-amended artificial soils are performed.

Bioavailability and cellular effects of metals on Lumbricus terrestris inhabiting volcanic soils

Whether the radial thickness (RT) of the chloragogenous tissue and intestinal epithelium of earthworms (Lumbricus terrestris) reflects the bioavailability of metals in soils was investigated in two areas, one with active volcanism (Furnas) and another with no volcanic activity since 3 million years ago (Santa Maria), in the Azores. Metal contents in soil samples and earthworms from the two areas were analyzed. Autometallography and measurements of the RT were performed in the chloragogenous tissue and intestinal epithelium. Earthworms from the active volcanic area demonstrated lower RT of chloragogenous tissue and intestinal epithelium as well as higher levels of bioavailable metals, especially Zn and Cd. Comparison of bioavailable metal contents between both areas suggests a higher risk for uptake of potentially toxic metals in the active volcanic area than in the non-active volcanic area, which is reflected by the lower RT of the chloragogenous tissue and intestinal epithelium in the former.

Biomarkers in mussels from a copper site gradient (Visnes, Norway): an integrated biochemical, histochemical and histological study

In the present work, mussels (Mytilus edulis) were transplanted into a copper (Cu) gradient in Visnes (Norway) for a period of 3 weeks during November 2003. Sites 1 and 2 showed similar low levels of Cu, site 3 had intermediate Cu levels and site 4 was the most polluted with Cu as confirmed by AAS of digestive gland tissue. Values of lysosomal membrane labilization period were significantly lower at sites 3 and 4 compared to sites 1 and 2. The volume density and size of lysosomes was significantly decreased at site 4. The volume density of neutral lipids was also significantly lower at site 4 compared with the rest of sites. The volume density of lipofuscins showed significantly higher values at sites 2 and 3 compared to the reference site 1. Similar results were obtained regarding bioavailable metal levels measured by autometallography. All together, results are indicative of exocytosis of metal-containing lysosomes and lipofuscins to the digestive tubule lumen in mussels from site 4. In fact, autometallographic metal deposits were detected in digestive tubule lumen, brown cells and stomach in site 4 mussels. In agreement, there was a loss of digestive cells in mussels from site 4 (atrophy of the digestive epithelium) and cell type replacement (diminished volume density of digestive cells and increased volume density of basophilic cells). In conclusion, selected biomarkers indicated that mussels transplanted to sites closest to the Cu mine showed significant differences in metal accumulation pattern and in organization of the digestive gland tissue. Finally, female mussels closest to the Cu mine showed advanced gametogenesis with higher gonad index and vitellogenin-like protein levels than mussels at sites 1 and 2.

Metal accumulation and apoptosis in the alimentary canal of Lumbricus terrestris as a metal biomarker

The chloragogenous tissue and the intestinal epithelium of adult earthworms, Lumbricus terrestris, sampled from sites with and without volcanic activity in the Azores were submitted to hematoxylin/eosin staining, autometallography and TUNEL-test in order to quantify the radial thickness of both tissues, their relative abundance of metals and apoptosis levels. Metals were visualized, through light microscopy, as black silver deposits (BSD) mostly in the chloragogenous tissue. The lowest radial thickness values of both tissues were found in the active volcanic sites, as well as the highest BSD and apoptosis levels. The BSD extent in the chloragogenous tissue, semi-quantified by stereology, exhibited a positive correlation with the apoptosis levels and a negative one with the radial thickness of both tissues. Thus, the variation of the radial thickness of both tissues, but especially of the chloragogenous tissue, which could reflect different cellular turnover rates caused by exposure to metals, is suggested as a biomarker of effect for metal exposure in terrestrial worms inhabiting volcanic environments.

Biomarkers in earthworms

Earthworms are believed to be so-called key species within ecosystems and are often exposed to a wide range of anthropogenic compounds released to the terrestrial environment. As a consequence, they may suffer from the toxicity of these compounds. For these and other reasons, earthworms have been used extensively in ecotoxicological studies. In recent years the use of other biological responses (biomarkers) to estimate either exposure or resultant effects of chemicals has received increased attention. Biomarkers address the question of bioavailability by only responding to the bioactive fraction. They may incorporate effects following exposure to a mixture of chemicals. Biomarkers may also reduce extrapolation of results from the laboratory to the field, as they may be applicable under both conditions. The present review has drawn together current knowledge on potential biomarkers in earthworms and appraised them in relation to basic requirements needed for supplying information relevant to devising satisfactory risk assessment. A wide range of potential biomarkers have been measured in earthworms, including DNA alteration, induction of metal-binding proteins (MTs and MBP), depression of ChE activity and other enzymatic responses, energy reserve responses, responses in neural impulse conductivity, lysosomal membrane stability, immunological responses, changes in sperm numbers, histopathological changes, and behavioral changes. Both organic and inorganic compounds have been included; however, for each biomarker the main emphasis historically has been placed on only a few chemicals. Dose-response relationships were in some cases observed. Little information is available on the linkage of the biomarker response to effects at population or community levels. The influence of other factors, biotic and abiotic, on the biomarker responses and their temporal duration have been only sporadically reported.