Metal bioaccumulation in spontaneously grown aquatic macrophytes in Fe-rich substrates of a passive treatment plant for acid mine drainage.

Some plants may thrive in polluted environments, accumulating high concentrations of metal/loids in their organs. This study investigates for the first time the bioaccumulation and translocation of metal/loids in Typha domingensis spontaneously grown in extremely Fe-rich substrates (38-44% of Fe2O3) from different components of an acid mine drainage disperse alkaline substrate passive treatment. Most metal/loids were predominantly accumulated in the roots over the aerial parts of the plant, with concentrations of 0.66-9.5% of Fe, 0.02%-0.18% of Al, 55-2589 mg kg-1 of Mg, 51-116 mg kg-1 of Zn, 17-173 mg kg-1 of Cu, and 5.2-50 mg kg-1 of Pb. Bioconcentration factors were mostly below 1 for metal/loids in the studied aneas (e.g. 0.03-0.47 for Cu, 0.10-0.73 for Zn, 0.04-0.28 for As, 0.07-0.55 for Pb, 0.27-055 for Cd, 0.24-0.80 for Ni), which evidences that T. domingensis behaves as an excluder species in these substrates. Translocation factors were below 1 for most elements (e.g. 0.01-0.42 for As, 0.06-0.50 for Pb, 0.24-0.65 for Cd, and 0.10-0.56 for Sb), except for Mn, Ni and in some cases for Tl, Cu and Zn, which indicates limited transfer of metals between plant tissues. Mineralogical and geochemical substrate properties are pointed out as the main factors responsible for the lower bioconcentration and translocation of potentially toxic elements. In addition, the oxidizing conditions existent in the pore water-root system may also limit the mobility of metals from Fe oxides and hydroxysulfates, the main component of the substrate. The formation of a Fe plaque inside the roots may also limit the transfer of metals to the aerial parts. The spontaneous occurrence of T. domingensis in the substrates of the acid mine drainage passive treatments is an environmental indicator of the efficiency of the system and could be used as a complementary polishing step, given the strong tolerance of this plants to high concentrations of metal/loids.

Consequences of sea level rise for high metal(loid) loads in the Ría of Huelva estuary sediments.

Ría of Huelva, located in southwestern Spain, is a highly metal(loid)-contaminated estuary system where sediments are exceeding action limits in an increasing order for Cd, Zn, Pb, Cu, and As. With a predicted sea level rise over the next 50 years, the estuary will be subject to flooding with brackish water or seawater. To evaluate the risk of metal(loid) mobilization under future climate scenarios, different locations along the estuary were sampled at different depths. Samples were flooded with river water, brackish water, and seawater under different short- and long-term laboratory setups. Potential metal(loid) mobilization showed that water quality standards for As, Pb, Zn, Ni, Cu, and Cd could be exceeded upon seawater flooding. However, metal(loid) mobilization was not predictable solely based on sediment loads. The driving factors for cation and anion mobility were identified to be mainly pH under low salinity and competitive desorption under high salinity conditions. Further drivers such as wave movement or labile C input in C-limited systems were found to enhance metal(loid) mobilization. Long-term flooding of intact sediment cores revealed that sea level rise will have different effects on the estuary system depending on duration of flooding. Short-term flooding in the near future will first affect alkaline sediments and enhance currently low cation mobilization, while anion mobilization due to reductive Fe dissolution will remain high. Once acidic sediments further inland are flooded with seawater, highest contaminant mobilization can be expected as high salinity will further enhance already high cation mobilization under acidic pH. Long-term flooding with seawater will neutralize the sediment pH and limit cation mobilization compared to acidic pH. However, the contaminant load stored in the estuary is so high that, extrapolating data obtained, mobilization could last for >1000 years, e.g. for As, Pb, and Al.

Trace metal mobility in sub-seabed sediments by CO2 seepage under high-pressure conditions.

Carbon capture and storage (CCS) is the third contributor to cumulative carbon emission reductions required by the second half of this century. Although this is a promising technology for reducing atmospheric CO2, it is only affordable if the confinement of the gas is guaranteed for hundreds of years. Hence, it is of paramount importance to figure out and predict the chemical and biological effects associated with potential CO2 leakage, to provide decision makers with a good basis for choosing technology and potential storage sites. To this end, a titanium reactor (1.4 m3) was used to study CO2 seepage under realistic sub-seabed conditions (30 bar pressure and 7 °C). The injection of CO2 was calibrated to decrease the pH value from 8.1 to 7.3, which may be the pH found near a leakage point. This pH value also coincides with predictions for near-future ocean pH under current CO2 emissions worldwide. The results from this study demonstrate that there are some elements, i.e., Fe, Co, Pb, Ce, Zn and Cu, present in deep marine sediments, that are strongly affected by the reduced pH levels related to CO2 addition. The dissolved concentrations of Fe, Pb and, to a lesser extent, Cr increased, due probably to weakening of the Fe/Mn shuttle by increased dissolved concentrations of CO2. Desorption processes from oxyhydroxide surfaces due to acidification may explain the release of Co, Ni and Ce observed during the experiment. The increased CO2 concentration also led to increased metal bioavailability, suggested by higher values for labile metal species. Conversely, Cd mobility seems not to be affected by CO2-associated acidification. It is concluded that the determination of those elements most affected by CO2-related acidification in a sub-seabed CO2 storage perimeter (i.e., sediment, sediment-water interface and water column) would be a simple and effective technique to verify suspected leakage.

Metal fractionation in marine sediments acidified by enrichment of CO2: A risk assessment.

Carbon-capture and storage is considered to be a potential mitigation option for climate change. However, accidental leaks of CO2 can occur, resulting in changes in ocean chemistry such as acidification and metal mobilization. Laboratory experiments were performed to provide data on the effects of CO2-related acidification on the chemical fractionation of metal(loid)s in marine-contaminated sediments using sequential extraction procedures. The results showed that sediments from Huelva estuary registered concentrations of arsenic, copper, lead, and zinc that surpass the probable biological effect level established by international protocols. Zinc had the greatest proportion in the most mobile fraction of the sediment. Metals in this fraction represent an environmental risk because they are weakly bound to sediment, and therefore more likely to migrate to the water column. Indeed, the concentration of this metal was lower in the most acidified scenarios when compared to control pH, indicating probable zinc mobilization from the sediment to the seawater.

Evaluation of the threat of marine CO2 leakage-associated acidification on the toxicity of sediment metals to juvenile bivalves.

The effects of the acidification associated with CO2 leakage from sub-seabed geological storage was studied by the evaluation of the short-term effects of CO2-induced acidification on juveniles of the bivalve Ruditapes philippinarum. Laboratory scale experiments were performed using a CO2-bubbling system designed to conduct ecotoxicological assays. The organisms were exposed for 10 days to elutriates of sediments collected in different littoral areas that were subjected to various pH treatments (pH 7.1, 6.6, 6.1). The acute pH-associated effects on the bivalves were observed, and the dissolved metals in the elutriates were measured. The median toxic effect pH was calculated, which ranged from 6.33 to 6.45. The amount of dissolved Zn in the sediment elutriates increased in parallel with the pH reductions and was correlated with the proton concentrations. The pH, the pCO2 and the dissolved metal concentrations (Zn and Fe) were linked with the mortality of the exposed bivalves.

Predicting the impacts of CO2 leakage from subseabed storage: effects of metal accumulation and toxicity on the model benthic organism Ruditapes philippinarum.

The urgent need to minimize the potential harm deriving from global climate change and ocean acidification has led governmental decision-makers and scientists to explore and study new strategies for reducing the levels of anthropogenic CO2. One of the mitigation measures proposed for reducing the concentration of atmospheric CO2 is the capture and storage of this gas in subseabed geological formations; this proposal is generating considerable international interest. The main risk associated with this option is the leakage of retained CO2, which could cause serious environmental perturbations, particularly acidification, in marine ecosystems. The study reported is aimed at quantifying the effects of acidification derived from CO2 leakage on marine organisms. To this end, a lab-scale experiment involving direct release of CO2 through marine sediment was conducted using Ruditapes philippinarum as a model benthic organism. For 10 days bivalves were exposed to 3 sediment samples with different physicochemical characteristics and at pre-established pH conditions (8.0-6.1). End points measured were: survival, burrowing activity, histopathological lesions, and metal accumulation (Fe, Al, Mn, Cu, and Zn) in whole body. Correlations analyses indicated highly significant associations (P < 0.01) between pH and the biological effects measured in R philippinarum, except for metal concentrations in tissues. Further research to understand and predict the biological and economic implications for coastal ecosystems deriving from acidification by CO2 leakages is urgently needed.

Studying the effect of CO2-induced acidification on sediment toxicity using acute amphipod toxicity test.

Carbon capture and storage is increasingly being considered one of the most efficient approaches to mitigate the increase of CO2 in the atmosphere associated with anthropogenic emissions. However, the environmental effects of potential CO2 leaks remain largely unknown. The amphipod Ampelisca brevicornis was exposed to environmental sediments collected in different areas of the Gulf of Cádiz and subjected to several pH treatments to study the effects of CO2-induced acidification on sediment toxicity. After 10 days of exposure, the results obtained indicated that high lethal effects were associated with the lowest pH treatments, except for the Ría of Huelva sediment test. The mobility of metals from sediment to the overlying seawater was correlated to a pH decrease. The data obtained revealed that CO2-related acidification would lead to lethal effects on amphipods as well as the mobility of metals, which could increase sediment toxicity.

Simulation of CO2 leakages during injection and storage in sub-seabed geological formations: metal mobilization and biota effects.

To assess the potential effects on metal mobilization due to leakages of CO2 during its injection and storage in marine systems, an experimental set-up was devised and operated, using the polychaete Hediste diversicolor as the model organism. The objective was to study the effects of such leakage in the expected scenarios of pH values between 8.0 and 6.0. Polychaetes were exposed for 10 days to seawater with sediment samples collected in two different coastal areas, one with relatively uncontaminated sediment as reference (RSP) and the other with known contaminated sediment (ML), under pre-determined pH conditions. Survival and metal accumulation (Al, Fe, Mn, Cu, Zn, As and Hg) in the whole body of H. diversicolor were employed as endpoints. Mortality was significant at the lowest pH level in the sediment with highest metal concentrations. In general, metal concentrations in tissues of individuals exposed to the contaminated sediment were influenced by pH. These results indicate that ocean acidification due to CO2 leakages would provoke increased metal mobilization, causing adverse side effects in sediment toxicity.