Metal Contamination Gradient Research Articles

Diversity and Structure of Soil Bacterial Communities in the Area of Non-ferrous Metal Plant Revealed by 16S rRNA Gene Retrieval

The goals of the study were to assess the diversity and structure of the bacterial communities within the soil depth along a gradient of heavy metal (HM) contamination and to identify indigenous bacterial species in the agricultural area of a non-ferrous metal plant KCM 2000 Group (Plovdiv) by using 16S rRNA gene retrieval. 16S rRNA gene clone libraries were constructed for nine samples, which were collected from two soil depths in June 2020. From each library, up to 100 clones were analysed and grouped into operational taxonomic units (OTUs) by restriction fragment length polymorphism (RFLP). The representatives of the OTUs were sequenced, followed by phylogenetic analysis. The results revealed that phyla Proteobacteria (11.11–71.43%) and Actinomycetota (3.57–33%) were the most abundant. Surface soils (12 phyla and 15 classes) were more diverse than subsurface ones (7 phyla and 12 classes). The lowest diversity at both phylum and class levels was calculated for the moderately contaminated soils from the two studied depths. Thirteen 16S rDNA sequences were identified to a species level, and they belonged to Proteobacteria, Actinomycetota and Firmicutes. This study highlighted that both HM contamination and soil depth caused shifts in diversity and structure of soil bacterial communities.

A novel approach to assess temporal baseline levels of trace metal contamination in the mussel M. galloprovincialis in the Mediterranean, Marmara and Black Seas

This study reports, for the first time, the baseline levels for fifteen trace metals in M. galloprovincialis tissue from around the Mediterranean, Marmara and Black Seas. The environmental quality in the surrounding seawater was assessed i.e., a mussel farm was investigated by using CF and DC indices, and the water quality was qualified as good for the aquacultural activities. A strong Cu-regulation in the transplanted mussels was observed and it ranged between 3.20 and 3.60 μg/g d.w. The highest bioavailability and bioconcentration of the particulate Fe fraction could present a health risk to consumers with a low risk level (1 < THQ < 9.9). Cr is considered the limiting metal for mussel consumption (< 2 kg/day). The metal contamination gradient was assessed using TEPI and TESVI indices that identified seven reference stations on the large scale and revealed that Cd is the most investigated metal in the literature databases, and found that Pb was the most bioavailable contaminant in the areas examined.

EDNA metabarcoding reveals shifts in sediment eukaryote communities in a metal contaminated estuary

Metal contamination is a global issue impacting biodiversity in urbanised estuaries. Traditional methods to assess biodiversity are time consuming, costly and often exclude small or cryptic organisms due to difficulties with morphological identification. Metabarcoding approaches have been increasingly recognised for their utility in monitoring, however studies have focused on freshwater and marine systems despite the ecological significance of estuaries. We targeted estuarine eukaryote communities within the sediments of Australia's largest urbanised estuary, where a history of industrial activity has resulted in a metal contamination gradient. We identified specific eukaryote families with significant correlations with bioavailable metal concentrations, indicating sensitivity or tolerance to specific metals. While polychaete families Terebellidae and Syllidae demonstrated tolerance to the contamination gradient, members of the meio- and microfaunal communities including diatoms, dinoflagellates and nematodes displayed sensitivities. These may have high value as indicators but are frequently missed in traditional surveys due to sampling limitations.

Metal bioavailable contamination engages richness decline, species turnover but unchanged functional diversity of stream macroinvertebrates at the scale of a French region

Freshwater ecosystems are the main source of water for sustaining life on earth, and the biodiversity they support is the main source of valuable goods and services for human populations. Despite growing recognition of the impairment of freshwater ecosystems by micropollutant contamination, different conceptual and methodological considerations can newly be addressed to improve our understanding of the ecological impact into these ecosystems. Here, we originally combined in situ ecotoxicology and community ecology concepts to unveil the mechanisms structuring macroinvertebrate communities along a regional contamination gradient. The novelty of our study lies in the use of an innovative biomonitoring approach (measurement of metal contents in caged crustaceans) allowing to quantify and compare on a regional scale the levels of bioavailable metal contamination to which stream communities are exposed. We were hence able to identify 23 streams presenting a significant gradient of bioavailable metal contamination within the same catchment area in the South West of France, from which we also obtained data on the composition of resident macroinvertebrate communities. Analyses of structural and functional integrity of communities revealed an unexpected decoupling between taxonomic and functional diversity of communities in response to bioavailable metal contamination. We show that despite the negative impact of bioavailable metal contamination exposure on taxonomic diversity (with an average species loss of 17% in contaminated streams), functional diversity is maintained through a process of non-random species replacement by functional redundant species at the regional scale. Such unanticipated findings call for a deeper characterization of metal-tolerant communities’ ability to cope with environmental variability in multi-stressed ecosystems.

Correlation between bacterial abundance, soil properties and heavy metal contamination in the area of non-ferrous metal processing plant, Southern Bulgaria

In the present study, the correlation between bacterial abundance and soil physicochemical properties along the heavy metal contamination gradient in the area of non-ferrous metal processing plant was assessed. Our results showed that bacterial abundance (number of heterotrophic bacteria and number of 16S rRNA gene copies) decreased with 45–56% (CFU) and 54–87% (16S rRNA gene) along the Zn, Pb and Cd contamination gradient. The total bacterial abundance (16S rRNA gene) increased exponentially in contrast to the abundance of heterotrophic bacteria. The reduction of bacterial abundance in heavily contaminated soil indicated that the soil properties (soil pH, total organic carbon, inorganic ions, soil texture) could modify the effects of heavy metals and the response of microorganisms to that stress in long-term contaminated soils.

Macrobenthic community responses to multiple environmental stressors in a subtropical estuary.

We assessed how multi- and univariate models reflect marine environmental health based on macrobenthic community responses to three environmental stressor categories: hydrodynamics, organic enrichment and metal contamination. We then compared the models with the benthic index AMBI (AZTI Marine Biotic Index). Macrobenthic community and physicochemical variables were sampled at 35 sites along Babitonga Bay, a subtropical estuary in Southern Brazil. Distance-based linear modelling identified depth, grain size and organic matter as well as Cu and Zn as key stressors affecting the macrobenthos. Using canonical analysis of principal coordinates (CAP), we developed three multivariate models based on the variability in community composition, creating stress gradients. The metal gradient showed better correlation with the benthic community. Sediment quality indices (Geoaccumulation Index and Contamination Factor) showed a low to moderate contamination status, with higher concentrations for Cr, Ni and Zn at the inner areas of the bay. According to AMBI, Babitonga Bay has a “good” environmental health status, and the AMBI values show stronger correlations with the hydrodynamic and organic enrichment gradients (r = 0.50 and r = 0.47) rather than the metal gradient (r = 0.29). Lumbrineridae polychaetes (not included in the AMBI list) and Scoloplos sp. were negatively related to the metal contamination gradient and were considered sensitive, while Sigambra sp., Magelona papillicornis, the gastropod Heleobia australis and species of the crustacean order Mysida were positively related to the gradient and considered tolerant to higher concentrations of metals in the sediment. Despite the inconsistency in the ecological classification provided by AMBI and its relationship with the metal gradient, our results suggest that the environmental quality was satisfactory for the studied gradients. The metal gradient showed the weakest correlation to AMBI. In such cases, the ecological classification of taxa by the index should be evaluated under the perspective of the action of inorganic genotoxic contaminants represented by metals.

Soil microbial community structure and functionality changes in response to long‐term metal and radionuclide pollution

SummaryMicrobial communities are essential for a healthy soil ecosystem. Metals and radionuclides can exert a persistent pressure on the soil microbial community. However, little is known on the effect of long‐term co‐contamination of metals and radionuclides on the microbial community structure and functionality. We investigated the impact of historical discharges of the phosphate and nuclear industry on the microbial community in the Grote Nete river basin in Belgium. Eight locations were sampled along a transect to the river edge and one location further in the field. Chemical analysis demonstrated a metal and radionuclide contamination gradient and revealed a distinct clustering of the locations based on all metadata. Moreover, a relation between the chemical parameters and the bacterial community structure was demonstrated. Although no difference in biomass was observed between locations, cultivation‐dependent experiments showed that communities from contaminated locations survived better on singular metals than communities from control locations. Furthermore, nitrification, a key soil ecosystem process seemed affected in contaminated locations when combining metadata with microbial profiling. These results indicate that long‐term metal and radionuclide pollution impacts the microbial community structure and functionality and provides important fundamental insights into microbial community dynamics in co‐metal‐radionuclide contaminated sites.

Intraspecific variability of responses to combined metal contamination and immune challenge among wild fish populations.

Wild organisms are increasingly exposed to multiple anthropogenic and natural stressors that can interact in complex ways and lead to unexpected effects. In aquatic ecosystems, contamination by trace metals has deleterious effects on fish health and commonly co-occurs with pathogens, which affect similar physiological and behavioral traits. However, the combined effects of metal contamination and parasitism are still poorly known. In addition, the sensitivity to multiple stressors could be highly variable among different fish populations depending on their evolutionary history, but this intraspecific variability is rarely taken into account in existing ecotoxicological studies. Here, we investigated i) the interactive effects of metal contamination (i.e., realistic mixture of Cd, Cu and Zn) and immune challenge mimicking a parasite attack on fish health across biological levels. In addition, we compared ii) the physiological and behavioral responses among five populations of gudgeon fish (Gobio occitaniae) having evolved along a gradient of metal contamination. Results show that single stressors exposure resulted in an increase of immune defenses and oxidative stress at the expense of body mass (contamination) or fish swimming activity (immune challenge). Multiple stressors had fewer interactive effects than expected, especially on physiological traits, but mainly resulted in antagonistic effects on fish swimming activity. Indeed, the immune challenge modified or inhibited the effects of contamination on fish behavior in most populations, suggesting that multiple stressors could reduce behavioral plasticity. Interestingly, the effects of stressors were highly variable among populations, with lower deleterious effects of metal contamination in populations from highly contaminated environments, although the underlying evolutionary mechanisms remain to be investigated. This study highlights the importance of considering multiple stressors effects and intraspecific variability of sensitivity to refine our ability to predict the effects of environmental contaminants on aquatic wildlife.

Ecotoxicity of trace elements to chicken GALLUS gallus domesticus exposed to a gradient of polymetallic-polluted sites.

Mining activity may cause heavy metal accumulation, which threatens human and animal health by their long-term persistence in the environment. This study aims to assess the impact of polymetallic pollution on chicken (Gallus domesticus) from old lead mining sites in northeast of Tunisia: Jebel Ressas (JR). Samples of soil and chickens were collected from five sites being ranked along a gradient of heavy metal contamination. Heavy metal loads were evaluated in soil samples and in chicken liver and kidney. Biochemical evaluation of oxidative stress parameters termed as Catalase (CAT), Glutathione-S-Transferase (GST), and Malondialdehydes (MDA) accumulation was monitored. Metallothionein protein level was assessed as a specific response to heavy metals. DNA alteration was achieved using MNi frequency in the investigated tissues. Finally, the evaluation of gene expression levels of CAT, GST, mt1, mt4, P53, bcl2, caspase3 and DNA-ligase was performed. Our data showed the highest loads of Cd, Cu, Zn and Pb in tissues of animals from site 3, being more pronounced in kidney. Biochemical data suggested a significant increase in antioxidant enzymes activities in all sites respect to control except in site 3 were CAT and GST were inhibited. DNA alteration was observed in all tissues being very pronounced in animals from site 3. Overall, transcriptomic data showed that genes involved in apoptosis were up-regulated in animals exposed to the most contaminated soils. Our data suggest that chicken and selected biomarkers offer a suitable model for biomonitoring assessment of heavy metals transfer through the food web in mining sites. Finally, the obtained results of heavy metals accumulation and related alterations should be carefully considered in view of the controversial relationship between distribution and toxicology of contaminants in exposed organisms.

Taxonomic and functional analysis of soil microbial communities in a mining site across a metal(loid) contamination gradient

AbstractSoil microorganisms surviving in mining sites have developed metal‐resistance mechanisms to biotransform metals. Their use as biofertilizers can improve phytoremediation efficiency in contaminated soils by reducing metal toxicity while promoting plant growth. We analysed through whole‐metagenome shotgun sequencing the composition, diversity and function of microbial communities present in a contaminated mine soil along a gradient of metals (As, Cu, Fe, Mn, Pb, Zn) to identify tolerant species carrying metal‐resistance functional genes that can be used in association with plants for phytoremediation. Soil samples were collected from an abandoned copper mine, across three areas with different levels of metal contamination (unaffected, moderately contaminated and highly contaminated). The relative abundance of Proteobacteria, especially genus Bradyrhizobium, increased in the highly contaminated area, whereas Actinobacteria dominated in the unaffected area. Archaea (Euryarchaeota) predominated in the moderately contaminated area, Haloarcula, Halobacterium and Halorubrum being the most abundant genera. The fungi Basidiomycota did not exhibit differences among the areas, whereas Ascomycota, especially the genus Aspergillus, increased in areas with low metal concentrations. Metal‐resistance genes associated with Fe (acn, furA, dpsA), Cu (cop‐unnamed, copF, actP, copA, mmco, cutO) and As (arsT, arsC, aioA/aoxB) metabolism were the most abundant and were affected by the gradient of soil contamination. Those associated with Cu predominated in the most contaminated area, whereas As and Fe genes were more abundant in the least contaminated. Among the carriers of these metal‐resistance genes, Bradyrhizobium diazoefficiens, Pseudomonas aeruginosa, Halorubrum trapanicum, Aspergillus fumigatus and A. fischeri were dominant in the most contaminated area. These species could give rise to promising biofertilizers to be used in association with suitable plants for the phytoremediation of contaminated mining sites.Highlights Metals affect differentially abundance, diversity and function of microorganisms in a mine soil. Proteobacteria dominated in contaminated areas and Actinobacteria in the less contaminated. Most abundant metal‐resistance genes were associated with Cu, As and Fe. Bradyrhizobium diazoefficiens and other species are promising biofertilizers for phytoremediation.

Fitness of two bivalves Saccostrea glomerata and Ostrea angasi exposed to a metal contamination gradient in Lake Macquarie, NSW Australia: Integrating subcellular, energy metabolism and embryo development responses

The fitness of two bivalves Saccostrea glomerata and Ostrea angasi exposed to a metal contamination gradient in Lake Macquarie, NSW Australia was assessed by measuring subcellular biomarkers (total antioxidant capacity, lipid peroxidation and lysosomal stability), energy metabolism responses and embryo development. Oyster tissue metal concentrations (Cu, Zn, Se, Cd and Pb) in both oyster species significantly increased over 31 days along the metal contamination gradient, but not in proportion to sediment metal concentrations. O. angasi had slightly higher metal concentrations but overall metal concentrations of both species were similar. In response to exposure to metal contaminated sediments, both oyster species showed a decrease in total antioxidant capacity, an increase in lipid peroxidation and decreased lysosomal membrane stability. Cellular Energy Allocation and energy consumption decreased with a corresponding usage of protein, lipid and glycogen stores at most sites. S. glomerata also demonstrated a significant reduction in embryo development. These responses demonstrated that exposure to metal-contaminated sediments impaired the fitness of S. glomerata and O. angasi in Lake Macquarie, NSW, Australia. To integrate and interpret the range of biomarkers measured in future studies, the effect of behavioural responses of bivalve mollusc to metal stress, bivalve closure and subsequent anaerobic metabolism should be evaluated to fully understand these responses.

Do metal contamination and plant species affect microbial abundance and bacterial diversity in the rhizosphere of metallophytes growing in mining areas in a semiarid climate?

Mining areas are low-quality habitats for macro- and microorganisms’ development, mainly due to the degradation of the soil quality by metal pollution. The present work aimed to analyze the influence of metal contamination and of plant species on the rhizospheric microbial communities of four indigenous metallophytes (Ononis natrix, Haloxylon scoparium, Peganum harmala, and Aizoon canariense) growing along a metal contamination gradient in Kettara mine near Marrakech, Morocco. In pyrrhotite mining areas (Kettara mine, Morocco), rhizosphere soil samples were collected from four predominant indigenous metallophytes (O. natrix, H. scoparium, P. harmala, and A. canariense) growing along a metal contamination gradient (ZC, control zone; Z1, high metal contamination; Z2, moderate metal contamination; Z3, low metal contamination). Microbial communities were analyzed by using microbial counts and by denaturing gradient gel electrophoresis (DGGE). The physicochemical properties (pH, conductivity, total organic carbon, nitrogen, P Olsen, and metal concentrations) of soils were also determined. The physicochemical analysis revealed that rhizospheric soils from Z1, Z2, and Z3 were relatively poor in nutrients as they presented low levels of total organic carbon and nitrogen, organic matter and available P. Moreover, these rhizospheric soils showed high concentrations of metals, especially Cu and Pb, which significantly reduced the abundance of the different groups of soil microorganisms (bacteria, fungi, and actinomycetes) and the activity of soil dehydrogenase. The analysis of bacterial communities by DGGE revealed that bacterial diversity was not negatively affected by metal contamination being higher in the most contaminated area (Z1). Overall, the microbial abundance, the composition, and the diversity of rhizospheric bacterial communities were more influenced by the environmental factors in sampling zones than by plant cover. Microbial counts and enzymatic activity were both systematically affected throughout the metal gradient, evidencing as good indicators of the harmful effects of anthropogenic disturbances in soils. H. scorparium and P. harmala proved to be good candidates for the development of phytotechnological programs aiming the revegetation of mining degraded areas.

Exposure to heavy metal-contaminated sediments disrupts gene expression, lipid profile, and life history traits in the midge Chironomus riparius

Despite the concern about anthropogenic heavy metal accumulation, there remain few multi-level ecotoxicological studies to evaluate their effects in fluvial ecosystems. The toxicity of field-collected sediments exhibiting a gradient of heavy metal contamination (Cd, Pb, and Zn) was assessed in Chironomus riparius. For this purpose, larvae were exposed throughout their entire life cycle to these sediments, and toxic effects were measured at different levels of biological organization, from the molecular (lipidomic analysis and transcriptional profile) to the whole organism response (respiration rate, shape markers, and emergence rate). Alterations in the activity of relevant genes, as well as an increase of storage lipids and decrease in membrane fluidity, were detected in larvae exposed to the most contaminated sediments. Moreover, reduced larval and adult mass, decrease of larval respiration rate, and delayed emergence were observed, along with increased mentum and mandible size in larvae and decreased wing loading in adults. This study points out the deleterious effects of heavy metal exposure at various levels of biological organization and provides some clues regarding the mode of toxic action. This integrative approach provides new insights into the multi-level effects on aquatic insects exposed to heavy metal mixtures in field sediments, providing useful tools for ecological risk assessment in freshwater ecosystems.

Soil microbial response to metal contamination in a vegetated and urban brownfield

The ubiquity of urban brownfields presents not only a challenge for environmental managers but also an opportunity to study the functional aspects of degraded ecosystems that are in close contact with human habitation. In this study, we investigate the soil microbial community response to heavy metal contamination at Liberty State Park (LSP), an urban brownfield in Jersey City, NJ, USA. Heavy metal contamination of the soils at LSP is heterogeneous, varying widely across site and among metals. We collected soils along a previously mapped gradient of metal contamination at LSP and sampled soil from a local and uncontaminated reference site (Hutcheson Memorial Forest (HMF)) for comparison. For all soils, we measured soil heavy metal concentrations, soil organic carbon content, bacterial density, and extracellular phosphatase activity as a proxy of ecosystem functioning. Additionally, we analyzed the microbial community composition using high-throughput sequencing. Data show that some sites within LSP have significantly higher phosphatase activity compared to HMF, indicating that some heavily contaminated LSP soils are highly functional. We also found that soil organic carbon and bacterial density have a significant and positive relationship with phosphatase activity. The microbial community analyses showed that the bacterial communities were sensitive to heavy metals and that the composition was significantly affected in particular by copper, zinc, and lead. The fungal communities, however, did not vary significantly with heavy metals. Our results shed important light on the composition and functioning of urban brownfield soils. A deeper understanding of these unique ecosystems is required for successful remediation, restoration and urban sustainability.

Does pollution influence small mammal diet in the field? A metabarcoding approach in a generalist consumer.

Mammals are mainly exposed to trace metals (TMs) via consuming contaminated food. Several studies have demonstrated relationships between metal concentrations in food and in animal tissues. However, potential effects of TMs on feeding behaviour of wildlife have been poorly documented under field conditions, despite experimental evidence showing that food selection is impacted by resource contamination. Here, we test the hypothesis that the diet of a generalist rodent, the wood mouse (Apodemus sylvaticus), is altered by soil TM contamination in the field. Wood mice were sampled in spring and in autumn along a gradient of soil contamination in the surroundings of a former smelter located in northern France. Available resources in the field were inventoried, and the diet of the animals was analysed using DNA "metabarcoding." We demonstrated that (a) relationship between the resource richness in the diet and their richness in the field was altered by soil metal contamination. Wood mice specialized their dietalong the gradient of soil metal contamination for both plant and invertebrate resources in spring. We also showed that (b) preference for Salicaceae, a plant family accumulating metals, decreased when soil contamination increased. These results suggest that environmental TM pollution could act as a force modulating trophic interactions in terrestrial food webs, thereby affecting wildlife exposure to contaminants by trophic route.

Cellular energy allocation analysis of multiple marine bivalves using near infrared spectroscopy

This paper proposes an alternative procedure for calculating Cellular Energy Allocation (CEA) in marine bivalve species. CEA is a measure of the difference in total energy available and energy consumption and is used to assess the health of organism fitness for growth and reproduction. In this study near infra-red spectral (NIRS) quantitative data-driven modelling techniques were applied to total energy available (total protein, lipid and glycogen content) and energy consumption (electron transport system activity (ETS)) of five marine bivalve species (Saccostrea glomerata, Ostrea angasi, Crassostrea gigas, Mytilus galloprovincialis and Anadara trapezia) to produce models for measuring each bioenergetic component and calculating CEA, a biomarker of energetic stress response. Comparison of predicted to measured data showed low prediction errors (RMSEP) and high ratio of predictive error to inter-quartile distance (RPIQ) values. RMSEP for protein, lipid, glycogen and ETS models were 8.7%, 6.8%, 7.6% and 12% of the dynamic range of the validation datasets respectively while RPIQ were 3.6, 5.2, 4 and 3.7 respectively. Conversion of model outputs to energetic equivalents and calculation of total energy stores as per the CEA method demonstrate a close relationship between measured and modelled results (105%±3%). These metrics indicate that the four energy models are accurate, robust and reliable for quantitative application to all five species within the sample variation of the energetic storage measures. Applying NIRS quantitative models using freeze dried tissue eliminates water interference in NIRS capture and provides improved sample homogeneity for both spectral capture and chemical analysis. This technique enables simultaneous analyses of protein, lipid, glycogen and ETS activity to be achieved with a much higher throughput of samples (100–200 samples daily) than conventional energetic storage analysis techniques. In addition, the technique is non-destructive to tissue samples and freeze dried samples can be stored for additional analyses. The value of CEA as a response measure in S. glomerata are included, with examples of changes in CEA over four seasons and the response of oysters to a known metal contamination gradient.

Maintenance of photosynthesis by Betula populifolia in metal contaminated soils

Improving our understanding of plant responses to elevated trace metal concentrations under field conditions will enhance restoration and urban greening practices in settings with contaminated soils. This study examined the effects of trace metal pollution on the leaf gas exchange rates of mature, field-grown Betula populifolia Marsh. (gray birch) trees, additionally assessing whether elevated temperature and drought compounded the effects of trace metal contamination. The study compared B. populifolia growing in areas of comparatively high and low trace metal loads (HML and LML, respectively) within a former rail yard at Liberty State Park in Jersey City, New Jersey, USA. Gas exchange parameters were determined monthly from May through September in 2014 and 2015 using a portable photosynthesis system. The effects of drought and high temperature were assessed during a short heat wave in July 2015 and via a manipulative experiment, respectively. During a few of the measurement months, some parameters differed significantly between the LML and HML groups. However, when considered over the entire study period, no significant differences in biophysical parameters were observed between groups. The photosynthetic capacity of B. populifolia thus appears to be fairly robust across this site's steep gradient of trace metal contamination. Nonetheless, leaf mass per unit area was significantly lower in the HML group, indicating that metal loads affected resource allocation within trees. Also, immediately following the heat wave in 2015, intrinsic water use efficiency declined significantly in the HML group, suggesting that extreme climatic conditions can have a disproportionate effect on the physiological performance of plants growing in metal contaminated soils.

Metal soil pollution differentially affects both the behaviour and exposure of A. caliginosa and L. terrestris: a mesocosm study

The effects on two earthworm species of a gradient of metal contamination in soil collected close to a 50-year-old lead recycling factory were investigated in mesocosms filled with soil sampled at three distances from the factory (10, 30 and 60 m). After 5 weeks of exposure, earthworm litter consumption and weight change were measured. Burrow systems were analysed using X-ray tomography, and water infiltration was measured. No significant differences in earthworm weight or activity were observed between mesocosms filled with soil from 30 and 60 m. In contrast, both earthworm species significantly lost weight and burrowed less in the soil sampled at 10 m. In the cores filled with the soil collected at 10-m distance, Aporrectodea caliginosa avoided the highly contaminated first layer (0–5 cm) and burrowed deeper whereas Lumbricus terrestris burrowed relatively more in this layer. We assume that these different reactions are associated with their ecological types. Epi-anecic earthworms forage litter at the soil surface, whereas endogeic earthworms are geophagous and thus are able to forage deeper. This was further corroborated by the bioaccumulation factors measured for each species: for L. terrestris, BAF values for Pb and Cd only decreased slightly in the 10-m soil correlating with their overall reduced activity. However, BAF values for A. caliginosa were 20-fold lower compared to those observed in soil from 30 and 60 m. These modifications in burrowing behaviour in the 10-m mesocosms resulted in a significant and marked decrease in water infiltration rates but only for L. terrestris.

Exposure of the freshwater bivalve Hyridella australis to metal contaminated sediments in the field and laboratory microcosms: metal uptake and effects.

Metal uptake and induced toxic effects on Hyridella australis were investigated by establishing 28 day exposure-dose-response relationships (EDR) of transplanted H. australis at four sites along a sediment metal contamination gradient in the mine affected Molonglo River, NSW. Laboratory exposure of this organism to the same sediments, collected from in situ sites, was run concurrently. Metal concentrations in whole organisms, individual tissues and sub-cellular tissue fractions were measured as organism metal dose. Total antioxidant capacity (TAOC), lipid peroxidation (MDA) and lysosomal membrane destabilisation (LMS) were measured as biological responses. H. australis accumulated significantly highertissue zinc concentrations compared to the other metals. In situ organisms at the mine affected sites accumulated more metals than organisms in laboratory microcosms. Accumulated zinc, cadmium and the total metal concentrations in whole organism tissues reflected exposure-dose relationships. Sub-cellular analysis showed that most of the accumulated metals, both in the field and laboratory exposed organisms, were detoxified over 28 days exposure. Clear exposure and dose dependent responses of decreased TAOC and measurable increases in MDA and LMS with increased metal exposure and dose were evident in H. australis caged in the river. In contrast, a dose-response relationship was only evident for cadmium in laboratory exposed organisms. Organisms caged at mine affected sites showed stronger EDR relationships than those exposed in laboratory microcosms as they were exposed to additional sources of dissolved zinc and cadmium. Exposure in laboratory microcosms underestimated metal uptake and effects, thus assessment of metal contaminated sediments should be undertaken "in situ".

Sediment-bound trace metals in Golfe-Juan Bay, northwestern Mediterranean: Distribution, availability and toxicity

The concentration, potential mobility, cation exchange capacity and toxicity of eight sediment-bound metals in Golfe-Juan Bay, France were examined. Results revealed significant spatial gradient of metal contamination along Golfe-Juan coast. The distribution and concentration of the metals appear to be influenced by the geochemical properties of the sediment, proximity to anthropogenic sources and general water circulation in the bay. The portion of trace metals found in the exchangeable, carbonate, oxidizable and reducible fractions of the sediment constitute 31%–58% of the total sediment-bound trace metal content, suggesting significant potential for remobilization of metals into the water column. Pb and Ni content of the sediment exceed the limits of the French marine sediment quality. Whole sediment extracts showed acute toxicity to marine rotifers. This study concludes that monitoring and management of sediment-bound trace metals in Golfe-Juan Bay are important so as not to underestimate their availability and risk to the marine ecosystems.