Converging hazard assessment of gold nanoparticles to aquatic organisms

The gold nanoparticles (Au-NPs) are being increasingly used because of their huge diversity of applications, and consequently, elevated levels in the environment are expected. However, due to their physico-chemical properties and functionalization a high variety of Au-NPs can be found, and complete toxicological information for each type of Au-NPs still lacks, and even, the toxicological information for the same species is sometimes contradictory. Therefore, hazard assessment should be done case by case. Hence, the objective of this study was to obtain ecotoxicological information of the same Au-NPs in aquatic organisms and to find a rationale for Au-NPs toxicity. For such a purpose, bare and hyaluronic acid capped Au-NPs (12.5 nm) along with Au-NPs bulk material were tested on freshwater algae, Daphnia and zebrafish. Results showed that while gold nanoparticles were found to be harmless to the tested organisms, the soluble gold showed to be toxic to algae and Daphnia, with an LC₅₀ between 1 and 2 mg L⁻¹. Comparing our results with those gathered in the literature, it appears that a common hazard assessment of Au-NPs on the studied organisms can be elucidated.     

Biowaste effects on soil and native plants in a semiarid ecosystem

Many soils of the Mediterranean region with a semiarid climate are subjected to progressive degradation as a result of water erosion. Biosolids and municipal solid wastes (MSW) were surface-applied once at three rates (40, 80, and 120 Mg ha(-1)) to different plots in a degraded semiarid ecosystem. The study was conducted to determine the effects of such applications on soil chemical properties and native vegetation over a three-year period. Soil N, P, and K initially increased with increasing biowaste application rates, but then decreased over time. Levels of Zn and Cu were higher in MSW than biosolid-treated plots, and increased in both years after application. Concentrations of soil Cd, Pb, Ni, and Cr did not change as a result of biowaste amendment in the study period. The growth of native plants was enhanced by the addition of biowastes. Total plant canopy and plant biomass increased significantly and remained higher in all treatments than in the control plot over the three-year period. The species richness of native plants decreased with increasing biowaste rates. Differences in the development of native plant communities between treatments were observed, and were more remarkable three years after biowaste application. Tissue N, P, K, Zn, and Cu levels increased with the biowaste application rate, but concentrations of tissue Pb, Cd, Ni, and Cr did not increase significantly. Biowastes applied at the rate of 80 Mg ha(-1) gave rise to the most favorable soil and native vegetation results while avoiding environmental risks.     

Short- and medium-term effects of experimental nitrogen fertilization on arthropods associated with Calluna vulgaris heathlands in north-west Spain

We studied the short- and medium-term effects of experimental nitrogen fertilization (3 and 15 months after the treatment) on the arthropods of Calluna vulgaris heathlands in NW Spain. Three heathland sites were selected with two permanent plots per site: control and fertilized. Ammonium nitrate fertilizer (56 kg N ha(-1) yr(-1)) was applied monthly and insects were caught using pitfall traps. We found mainly species-level responses to nitrogen addition. Seven species (e.g. Lochmaea suturalis) showed a consistent trend (benefited or harmed) in both periods and were proposed as possible reliable indicators of the effects of nitrogen deposition in these ecosystems. We also found variable arthropod trophic-group responses: (a) herbivores (leaf beetles, true bugs) increased in abundance on a short-term scale; (b) predators (carabid beetles, true bugs) showed opposite and less clear responses in both periods. Further long-term studies are needed to determine the mechanisms underlying the observed arthropod responses.     

Tolerance (PICT) of the bacterial communities to copper in vineyards soils from Spain

To detect effects of Cu pollution, the Cu tolerance of soil bacterial communities extracted from several vineyards located in NW Spain was measured. Bacterial community tolerance was estimated by means of the thymidine (TdR) and leucine (Leu) incorporation techniques using either IC(50) values (the log of the metal concentration that reduced incorporation to 50%) or the percentage of activity at one specific Cu concentration (10(-6) mol L(-1)). The tolerance measurements by the TdR incorporation technique were similar to those obtained by the Leu incorporation method, indicating that the two methods were equivalent in terms of suitability for detecting the toxicity of Cu to soil bacterial communities. The two tolerance indices considered (IC50 values and percentage of activity) were closely correlated (r = 0.975, P < 0.001), showing that both were equally good in measuring Cu tolerance of the bacterial community. An increased bacterial community tolerance to Cu, indicating a pollution effect, was observed in vineyard soils with more than 100 mg Cu kg(-1) soil. Thus, the long-term use of Cu in vineyards has a toxic effect on the soil bacterial community, resulting in an increased tolerance. An effect of increased levels of Cu could not be detected when measuring bacterial community activity, pointing to the increased sensitivity to detect toxicity in field studies using tolerance measurements.     

Arsenic uptake and accumulation in curly endives (Cichorium endivia L.) irrigated with contaminated water

Arsenic accumulation in vegetables for direct human consumption represents a concern for food safety purposes. This potential problem can be of economic importance particularly in much appreciated, high-quality horticultural products. In this work, a greenhouse set of experiments were conducted to evaluate possible phytotoxic effects and arsenic accumulation in the production of curly endives with arsenic contaminated water.Two concentration levels (0.5 mg/L and 1.0 mg/L) and two arsenic species (As+3 and As+5) were considered. Dry mass production tended to be reduced as As+3 concentration increased in irrigation water. However, As+5 treatments did not show significant dry mass production differences with a blank (control experiment). As accumulation in plant increased with As concentration in irrigation waters, following a linear trend. Nevertheless, the increase of accumulated As was not statistically significant for As+5 at 0.5 mg/L. Calculated biological absorption coefficients resulted in higher than previous values reported in the literature, which was attributed here to the source of arsenic (irrigation water). Considering field values for As+5/As+3 ratio and averaged concentrations in water, the obtained results support that there is not a short-or medium-term risk to food safety in the curly endive crop in the region of Castilla y León (Spain).     

Efficiency of a protected-area network in a Mediterranean region: a multispecies assessment with raptors

Three different systems of designating protected areas in a Mediterranean region in southeastern Spain were studied, referring to their effectiveness and efficiency for protecting both the breeding territories and the suitable habitat of a set of ten raptor species. Taking into consideration the varying degrees of endangerment of these species, a map of multispecies conservation values was also drawn up and superimposed on the three protected-area systems studied. In order to compare the levels of protection afforded by the three systems, we considered two indices that measured their relative effectiveness and efficiency. The effectiveness estimated the proportion of territories or optimal habitat protected by the networks while efficiency implicitly considered the area of each system (percentage of breeding territories or optimal habitat protected per 1% of land protected). Overall, our results showed that the most efficient system was that formed by the set of regional parks and reserves (17 protected breeding territories per 100 km²), although, given its small total area, it was by far the least effective (only protecting the 21% of the breeding territories of all species and 17% of the area of high conservation value). The systems formed by the Special Protection Areas (designated under the EU “Birds Directive”) and by the Special Conservation Areas (designated under the EU “Habitats Directive”) notably increased the percentages of protected territories of all species (61%) and area of high conservation value (57%), but their efficiency was not as high as expected in most cases. The overall level of protection was high for all species except for the Lesser Kestrel (Falco naumanni), an endangered falcon that inhabits pseudo-steppe and traditional agricultural habitats, which are clearly underrepresented in the protected-area network of the study region.     

Responses of evergreen and deciduous Quercus species to enhanced ozone levels

Plants of one evergreen oak (Quercus ilex) and three deciduous oaks (Q. faginea, with small leaves; Q. pyrenaica and Q. robur, with large leaves) were exposed both to filtered air and to enhanced ozone levels in Open-Top Chambers. Q. faginea and Q. pyrenaica were studied for the first time. Based on visible injury, gas exchange, chlorophyll content and biomass responses, Q. pyrenaica was the most sensitive species, and Q. ilex was the most tolerant, followed by Q. faginea. Functional leaf traits of the species were related to differences in sensitivity, while accumulated ozone flux via stomata (POD_1.6) partly contributed to the observed differences. For risk assessment of Mediterranean vegetation, the diversity of responses detected in this study should be taken into account, applying appropriate critical levels.     

Fertilization of maize with compost from cattle manure supplemented with additional mineral nutrients

An alternative approach for cattle manure management on intensive livestock farms is the composting process. An industrial-scale composting plant has been set up in northwest Spain for producing compost from cattle manure. Manure composting involved an increase in pH, electrical conductivity (EC), cation exchange capacity (CEC) and NO3(-)--N concentration, and a decrease in temperature, moisture content, organic matter (OM) content, NH4+--N concentration and C/N ratio. Cu, Zn and Ni concentrations increased due to the reduction of pile mass during the composting process. The resulting compost was applied to a field to study the viability of applying this compost combined with a nitrogen mineral fertilizer as a replacement for the mineral fertilization conventionally used for maize (Zea mays L.). The thermophilic phase of the composting process was very prolonged in the time, which may have slowed down the decomposition of the organic matter and reduced the nitrification process, leading to an over-short maturation phase. The humification and respirometric indexes, however, determined immediately after compost application to the soil, showed it to be stable. Compost application did not decrease the grain yield. A year later, soil pH, OM content and CEC were higher with the compost treatment. Total P, K, Ca and Na concentrations in compost-amended plots were higher than in mineral-fertilized ones, and no significant differences between treatments were found in soil concentrations of NH4+--N,NO3- --N, available P, Mg and B. Compost caused no heavy metal pollution into the soil. Therefore, this compost would be a good substitute for the mineral fertilizers generally used for basal dressing in maize growing.     

Trace elements in biodeposits and sediments from mussel culture in the Ria de Arousa (Galicia, NW Spain)

The trace elements present at highest concentrations were Cr and Zn, which probably originated from the dumping of effluent from a tanning factory. High proportions of these two elements were associated with the residual fraction. Biodeposits and sediments showed high concentrations of Cd and Pb in the reactive fraction, with a high proportion of the concentration in the reactive fraction being associated with carbonates. Nickel showed a higher degree of pyritization than the previous elements, although most of the Ni was associated with the residual and reactive fractions. Arsenic, Hg and Cu showed high degrees of pyritization, particularly below a depth of 5 cm. The results demonstrate that those elements with a high degree of pyritization may be released into the water through oxidation of the metal sulphides that they form when in suspension in oxic sea water, with the subsequent risk of increased bioavailability to benthic fauna.