José Antonio Rodríguez Martín

Effect of mine tailing on the spatial variability of soil nematodes from lead pollution in La Union (Spain)

The Cartagena-La Union mining district, exploited since the end of the 3rd century BC, was one of the worlds largest lead producers in the 19th century. Although activity ceased in 1991, today mining residues pose a huge pollution problem. This study characterises lead contents (total and DPTA) and other soil parameters (N, P, K, pH, SOM, CaCO3, granulometric fraction, etc.) using multivariate geostatistical methods in relation to nematode diversity. In this work, trophic groups and metabolic footprints of soil nematodes were measured using 193 samples from the mining, natural and agricultural areas in this district. We explored the relationship between soil health and nematode communities. High lead concentrations were quantified: mean 8,500 mg kg(-1) for total and 340 mg kg(-1) for DPTA in this mining area. Although nematode diversity was broad (81 taxa), their diversity, abundance and metabolic footprints significantly reduced in the mining area. Significant differences in the nematode community structure were observed, and the relative abundance of predators was sensitive to mine and agricultural activities, whilst omnivores reduced only in the agricultural area, and bacterial feeders exhibited a differential response to both anthropogenic disturbances. The total abundance of nematodes, trophic groups and c-p groups correlated negatively with soil Pb contents, and a positive relationship was found with SOM and N, P and K contents.

Transgenic nematodes as biosensors for metal stress in soil pore water samples

Caenorhabditis elegans strains carrying stress-reporter green fluorescent protein transgenes were used to explore patterns of response to metals. Multiple stress pathways were induced at high doses by most metals tested, including members of the heat shock, oxidative stress, metallothionein (mtl) and xenobiotic response gene families. A mathematical model (to be published separately) of the gene regulatory circuit controlling mtl production predicted that chemically similar divalent metals (classic inducers) should show additive effects on mtl gene induction, whereas chemically dissimilar metals should show interference. These predictions were verified experimentally; thus cadmium and mercury showed additive effects, whereas ferric iron (a weak inducer) significantly reduced the effect of mercury. We applied a similar battery of tests to diluted samples of soil pore water extracted centrifugally after mixing 20% w/w ultrapure water with air-dried soil from an abandoned lead/zinc mine in the Murcia region of Spain. In addition, metal contents of both soil and soil pore water were determined by ICP-MS, and simplified mixtures of soluble metal salts were tested at equivalent final concentrations. The effects of extracted soil pore water (after tenfold dilution) were closely mimicked by mixtures of its principal component ions, and even by the single most prevalent contaminant (zinc) alone, though other metals modulated its effects both positively and negatively. In general, mixtures containing similar (divalent) metal ions exhibited mainly additive effects, whereas admixture of dissimilar (e.g. trivalent) ions often resulted in interference, reducing overall levels of stress-gene induction. These findings were also consistent with model predictions.

Use of transgenic GFP reporter strains of the nematode Caenorhabditis elegans to investigate the patterns of stress responses induced by pesticides and by organic extracts from agricultural soils

As a free-living nematode, C. elegans is exposed to various pesticides used in agriculture, as well as to persistent organic residues which may contaminate the soil for long periods. Following on from our previous study of metal effects on 24 GFP-reporter strains representing four different stress-response pathways in C. elegans (Anbalagan et al. Ecotoxicology 21:439–455, 2012), we now present parallel data on the responses of these same strains to several commonly used pesticides. Some of these, like dichlorvos, induced multiple stress genes in a concentration-dependent manner. Unusually, endosulfan induced only one gene (cyp-34A9) to very high levels (8–10-fold) even at the lowest test concentration, with a clear plateau at higher doses. Other pesticides, like diuron, did not alter reporter gene expression detectably even at the highest test concentration attainable, while others (such as glyphosate) did so only at very high concentrations. We have also used five responsive GFP reporters to investigate the toxicity of soil pore water from two agricultural sites in south-east Spain, designated P74 (used for cauliflower production, but significantly metal contaminated) and P73 (used for growing lettuce, but with only background levels of metals). Both soil pore water samples induced all five test genes to varying extents, yet artificial mixtures containing all major metals present had essentially no effect on these same transgenes. Soluble organic contaminants present in the pore water were extracted with acetone and dichloromethane, then after evaporation of the solvents, the organic residues were redissolved in ultrapure water to reconstitute the soluble organic components of the original soil pore water. These organic extracts induced transgene expression at similar or higher levels than the original pore water. Addition of the corresponding metal mixtures had either no effect, or reduced transgene expression towards the levels seen with soil pore water only. We conclude that the main toxicants present in these soil pore water samples are organic rather than metallic in nature. Organic extracts from a control standard soil (Lufa 2.2) had negligible effects on expression of these genes, and similarly several pesticides had little effect on the expression of a constitutive myo-3::GFP transgene. Both the P73 and P74 sites have been treated regularly with (undisclosed) pesticides, as permitted under EU regulations, though other (e.g. industrial) organic residues may also be present.

Effect of soil properties, heavy metals and emerging contaminants in the soil nematodes diversity.

Among soil organisms, nematodes are seen as the most promising candidates for bioindications of soil health. We hypothesized that the soil nematode community structure would differ in three land use areas (agricultural, forest and industrial soils), be modulated by soil parameters (N, P, K, pH, SOM, CaCO3, granulometric fraction, etc.), and strongly affected by high levels of heavy metals (Cd, Pb, Zn, Cr, Ni, Cu, and Hg) and emerging contaminants (pharmaceuticals and personal care products, PPCPs). Although these pollutants did not significantly affect the total number of free-living nematodes, diversity and structure community indices vastly altered. Our data showed that whereas nematodes with r-strategy were tolerant, genera with k-strategy were negatively affected by the selected pollutants. These effects diminished in soils with high levels of heavy metals given their adaptation to the historical pollution in this area, but not to emerging pollutants like PPCPs.

Factors Controlling the Spatial Variability of Mercury Distribution in Spanish Topsoil

This study characterized the sources and scales of mercury variability in agricultural soils of the river Ebro (9.5 million ha) using geostatistical methods and data from 624 samples. The Ebro basin (20% of Spanish land mass) is an important agricultural area that is industrialized. Spatial analysis was done on a local scale (20 km) and indicated that high Hg concentrations were related to mining and specific agronomic practices, such as sewage effluents from irrigation. The intermediate scale (100 km) was associated with mercury from atmospheric deposition (mining, smelting, and industrial activities). The regional scale (220 km) corresponded to mineralogical structure and bedrock influence. The analysis demostrates that while geographical and geochemical processes and anthropogenic influences, such as industrialization and agricultural practices, can influence the content and distribution of mercury in the valley, the calcareous nature of the soils (alkaline pH and low organic matter) minimize the effect of the mercury load.

Entomopathogenic nematode food webs in an ancient, mining pollution gradient in Spain.

Mining activities pollute the environment with by-products that cause unpredictable impacts in surrounding areas. Cartagena-La Unión mine (Southeastern-Spain) was active for >2500years. Despite its closure in 1991, high concentrations of metals and waste residues remain in this area. A previous study using nematodes suggested that high lead content diminished soil biodiversity. However, the effects of mine pollution on specific ecosystem services remain unknown. Entomopathogenic nematodes (EPN) play a major role in the biocontrol of insect pests. Because EPNs are widespread throughout the world, we speculated that EPNs would be present in the mined areas, but at increased incidence with distance from the pollution focus. We predicted that the natural enemies of nematodes would follow a similar spatial pattern. We used qPCR techniques to measure abundance of five EPN species, five nematophagous fungi species, two bacterial ectoparasites of EPNs and one group of free-living nematodes that compete for the insect-cadaver. The study comprised 193 soil samples taken from mining sites, natural areas and agricultural fields. The highest concentrations of iron and zinc were detected in the mined area as was previously described for lead, cadmium and nickel. Molecular tools detected very low numbers of EPNs in samples found to be negative by insect-baiting, demonstrating the importance of the approach. EPNs were detected at low numbers in 13% of the localities, without relationship to heavy-metal concentrations. Only Acrobeloides-group nematodes were inversely related to the pollution gradient. Factors associated with agricultural areas explained 98.35% of the biotic variability, including EPN association with agricultural areas. Our study suggests that EPNs have adapted to polluted habitats that might support arthropod hosts. By contrast, the relationship between abundance of Acrobeloides-group and heavy-metal levels, revealed these taxa as especially well suited bio-indicators of soil mining pollution.

Using fuzzy clustering algorithms to describe the distribution of trace elements in arable calcareous soils in northwest Iran

Accumulation of trace elements in arable soils is an important global hazard worldwide. In this research, the available content of Zn, Fe, B, Co, Cu, Mn, Mo and other soil parameters (pH, organic carbon content, carbonates and electrical conductivity) were analysed in northwest Iran. Concentration levels of trace elements were relatively low in areas with high pH values and low organic matter content, and only the Mo value exceeded the reference threshold. Based on the correlation among the elements, two datasets were produced. The first consists of Fe and Mn data, while the second contains Zn, B, Co, Cu and Mo data. Two fuzzy clustering approaches, Fuzzy C-means (FCM) and Gustafson–Kessel (GK), were applied for clustering both datasets. Multiple accumulation of trace elements was investigated from the clustering results and then visualized in spatial regionalization maps. The fuzzy clustering evaluating indices showed that the GK method was more appropriate than FCM for clustering datasets. The results revealed that the first and second datasets were divided into seven and six clusters, respectively. Fuzzy clustering analyses combined with geostatistical methods were used to map the spatial variability of each cluster. This method enabled the monitoring of multiple metal accumulation in large agricultural soils.

Wood and bark of Pinus halepensis as archives of heavy metal pollution in the Mediterranean Region

Natural levels of heavy metals (HM) have increased during the industrial era to the point of posing a serious threat to the environment. The use of tree species to record contamination is a well-known practice. The objective of the study was to compare HM levels under different pollution conditions: a) soil pollution due to mining waste; b) atmospheric pollution due to coal-fired power plant emissions. We report significant HM enrichment in Pinus halepensis tissues. Near a burning power plant, Pb content in a tree wood was 2.5-fold higher that in natural areas (no pollution; NP). In mining areas, Cd content was 25-fold higher than NP. The hypothesis that HM contents in tree rings should register pollution is debatable. HM uptake by pines from soil, detoxification mechanisms and resuspended local soil dust is involved in HM contents in wood and bark.

Trace elements concentrations in soil, desert-adapted and non-desert plants in central Iran: Spatial patterns and uncertainty analysis

The concentrations of Cd, Cr and Pb in soil samples and As, Cd, Cr and Pb in plant specimens were analyzed in an arid area in central Iran. Plants were categorized into desert-adapted (Haloxylon ammodendron, Atraphaxis spinosa and Artemisia persica) and non-desert species. It was found that the trace element (TE) accumulating potential of the desert species (Haloxylon ammodendron and Artemisia persica) with a mean value of 0.1 mg kg-1 for Cd was significantly higher than that of the majority of the non-desert species with an average of 0.05 mg kg-1. Artemisia also had a high As accumulating capability with a mean level of 0.8 mg kg-1 in comparison with an average of 0.2 mg kg-1 for most of the other plant species. The mean values of Cr and Pb in Haloxylon ammodendron and Artemisia persica were 5 and 3 mg kg-1, respectively. Among the desert-adapted plants, Atraphaxis proved to be a species with high Cr and Pb accumulating potential, as well. The geoaccumulation index and the overall pollution scores indicated that the highest environmental risk was related to Cd. Different statistical analyses were used to study the spatial patterns of soil Cd and their connections with pollution sources. The variogram was estimated using a classical approach (weighted least squares) and was compared with that of the posterior summaries that resulted from the Bayesian technique, which lay within the 95% Bayesian credible quantile intervals (BIC) of posterior parameter distributions. The prediction of cadmium values at un-sampled locations was implemented by multi-Gaussian kriging and sequential Gaussian simulation methods. The prediction maps showed that the region most contaminated by Cd was the north-eastern part of the study area, which was linked to mining activities, while agricultural influence contributed less in this respect.