M.E. Pereira

Mercury pollution in Ria de Aveiro (Portugal): a review of the system assessment

The Ria de Aveiro (Portugal) is a coast al lagoon adjacent to the Atlantic Ocean and it has an inner bay (Laranjo bay) that received a highly contaminated effluent discharged by a mercury cell chlor-alkali plant from the 1950s until 1994. The aim of this study is to review in a holistic way several research studies that have been carried out in the Ria de Aveiro, in order to evaluate the remobilization of the mercury accumulated within the system and the recovery of the lagoon. The spatial distribution of the total mercury in the surrounding terrestrial environment has also been considered. Results indicate that the main mercury contamination problems in the Ria de Aveiro are confined to the Laranjo bay. Mercury export to the coastal waters and its impact on the nearshore compartments (water column, sediment and biota) are low. No direct effects of the mercury from nearby industrial activities were detected in Aveiro’s urban soils, although historical mercury contamination is still affecting soil quality in the immediate vicinity of the chlor-alkali plant, located in Estarreja. Moreover, macrophyte harvesting for human direct or indirect use and the consumption of mussels, crabs and the sea bass from the Laranjo bay may constitute a health risk. Further studies focusing on developing skills for the restoration of the ecosystem are presently underway.

Antioxidant and biotransformation responses in Liza aurata under environmental mercury exposure - Relationship with mercury accumulation and implications for public health

This study was carried out in the Laranjo basin (Ria de Aveiro, Portugal), an area impacted by mercury discharges. Liza aurata oxidative stress and biotransformation responses were assessed in the liver and related to total mercury (Hgt) concentrations. A seasonal fish survey revealed a sporadic increase in total glutathione (GSHt) and elevated muscle Hgt levels, although Hg levels did not exceed the EU regulatory limit. As a complement study, fish were caged for three days both close to the bottom and on the water surface at three locations, and displayed higher Hgt levels accompanied by increased GSHt content and catalase activity as well as EROD activity inhibition. The bottom group displayed higher hepatic Hgt and GSHt contents compared with the surface group. Globally, both wild and caged fish revealed that the liver accumulates higher Hgt concentrations than muscle and, thus, better reflects environmental contamination levels. The absence of peroxidative damage in the liver can be attributed to effective detoxification and antioxidant defense.

Tidal export of particulate mercury from the most contaminated area of Aveiro's Lagoon, Portugal

Mercury pollution is a regional problem in the Aveiros Lagoon. During 4 decades, a remote branch (Estarreja Channel) has received a discharge of mercury from a chlor-alkali plant, that is spread in the Laranjo Basin. Of special interest is the dispersion of mercury from these areas to the Lagoon. This work is a first attempt to quantify the net flux of particulate mercury from the most contaminated basin (Laranjo). Measurements of current intensity, suspended particulate matter and particulate mercury were carried out at two sampling stations over a spring tidal cycle, in April 1994. Based on a mass balance calculation at two stations, at the end of Estarreja Channel (F1) and near the outlet of Laranjo Basin (F2), the net tidal fluxes of particulate anthropogenic mercury were estimated: 0.4 g of mercury enter the Laranjo Basin and 94.5 g of particulate mercury escape the Basin. These results indicate that mercury from the most contaminated area continues to be dispersed, predominantly through the particulate fraction, to the rest of the Lagoon.

Evaluation of an approach for the characterization of reactive and available pools of twenty potentially toxic elements in soils: Part I – The role of key soil properties in the variation of contaminants’ reactivity

Harmful effects of potentially toxic elements (PTEs) in soils relate to their geochemically reactive fraction. To assess the degree of the reactivity, specific extractions or models are needed. Here we applied a 0.43 M HNO(3) chemical extraction to assess reactive pools of a broad range of PTEs in 136 contaminated and non-contaminated soils. Furthermore we derived Freundlich-type models based on commonly available soil properties (pH, organic carbon and clay) as well as extended models that used other properties such as amorphous Al and Fe oxides and evaluated their possible use in risk assessment. The approach allowed to predict the reactivity of As, Hg, Co, U, Ba, Se, Sb, Mo, Li, Be (r(2): 0.55-0.90) elements not previously included in such studies, as well as that of Cd, Zn, Cu, Pb, Ni and Cr (r(2): 0.73-0.90). The inclusion of pH, organic carbon and clay improved the performance of all models except for Be and Mo, although the role of clay is not completely clear and requires further investigation. The ability of amorphous metal oxides to affect the reactivity of As, Hg, Cu, Ni, Cr, Sb, Mo and Li was expressed by the models in agreement with known geochemical processes leading to the retention of PTEs by the solid matrix. Hence, such approach can be a useful tool to account for regional differences in soil properties during the identification of risk areas and constitute a significantly more powerful tool than the analysis of total pools of PTEs in soils.

A review of regulatory decisions for environmental protection: Part I — Challenges in the implementation of national soil policies

Since many soil studies have already revealed the possible risks to human health and the environment arising from contaminated soils it is therefore crucial to preserve soil quality under current and future conditions. In the last three decades a number of countries already introduced national policies and practices for the management of contaminated sites, and in 2002, an EU Thematic Strategy for Soil Protection was proposed by the European Commission. In this paper we review and analyse several national contaminated land policy regimes already in place in order to assess common elements and to identify specific needs in the development of national soil policies. We propose a framework that combines the D-P-S-I-R structure of policy evaluation with the Source-Pathway-Receptor approach to health risk assessment to support the development of effective country specific regulatory decisions for managing contaminated land in countries where these are yet to be implemented. The framework proposed allows decision makers to effectively use available information and to identify existing data gaps. As a result it is apparent that while there are technical aspects of site characterisation, risk assessment and remediation processes that could be commonly implemented at an EU level there are certain trans-scientific aspects that require political choices and need to be customized by EU Member States.

Brain as a critical target of mercury in environmentally exposed fish (Dicentrarchus labrax)--bioaccumulation and oxidative stress profiles.

Although mercury is recognized as a potent neurotoxicant, information regarding its threat to fish brain and underlying mechanisms is still scarce. In accordance, the objective of this work was to assess vulnerability of fish to mercury neurotoxicity by evaluating brain pro-oxidant status in wild European sea bass (Dicentrarchus labrax) captured in an estuarine area affected by chlor-alkali industry discharges (Laranjo Basin, Ria de Aveiro, Portugal). To achieve this goal, brain antioxidant responses such as catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferase (GST) activities and total glutathione (GSHt) content were measured. Additionally, damage was determined as lipid peroxidation. To ascertain the influence of seasonal variables on both mercury accumulation and oxidative stress profiles, surveys were conducted in contrasting conditions-warm and cold periods. In the warm period, brain of fish from mercury contaminated sites exhibited ambivalent antioxidant responses, viz. higher GR activity and lower CAT activity regarded, respectively, as possible signs of protective adaptation and increased susceptibility to oxidative stress challenge. Though the risk of an overwhelming ROS production cannot be excluded, brain appeared to possess compensatory mechanisms and was able to avoid lipid peroxidative damage. The warm period was the most critical for the appearance of oxidative damage as no inter-site alterations on oxidative stress endpoints were detected in the cold period. Since seasonal differences were found in oxidative stress responses and not in mercury bioaccumulation, environmental factors affected the former more than the latter. This work increases the knowledge on mercury neurotoxicity in feral fish, highlighting that the definition of critical tissue concentrations depends on environmental variables.

Antioxidant system breakdown in brain of feral golden grey mullet (Liza aurata) as an effect of mercury exposure

Although brain has been recognized as a primary target for mercury toxicity in mammals, the effects of this metal in fish brain are scarcely described. Thus, the main objective of this study was to assess the mercury threat to feral fish (Liza aurata) by estimating the antioxidant defenses and peroxidative damage in brain, keeping in mind the association with mercury accumulation. Sampling was carried out in an estuarine area historically affected by discharges from a chlor-alkali industry—Laranjo Basin (Ria de Aveiro, Portugal). Total mercury (T-Hg) in brain increased towards the contamination source, clearly indicating mercury exposure. An overall antioxidant depletion was verified in brain of fish collected at the mercury-contaminated stations, since total glutathione content and the studied antioxidant enzymes (catalase—CAT, glutathione peroxidase—GPx, glutathione-S-transferase—GST and glutathione reductase—GR) significantly decreased. In addition, this breakdown of the redox-defense system was significantly correlated with the accumulated T-Hg levels. Unexpectedly, fish exhibited unaltered lipid peroxidation levels, pointing out a higher propensity of mercury to inhibit enzymes than to oxidatively damage lipids in the brain. Nevertheless, an increased susceptibility of the fish’s brain was identified, leaving the organ more vulnerable to oxidative stress-related challenges. Overall, the current findings provide information to better understand mechanisms of mercury neurotoxicity in fish.

Water-soluble fraction of mercury, arsenic and other potentially toxic elements in highly contaminated sediments and soils.

The water-soluble contents of mercury, arsenic and other potentially toxic elements in highly contaminated sediment and soil samples from Portugal were determined. Mercury and arsenic concentrations were detectable and reproducible among replicate experiments. Despite the acidic pH, the low organic carbon content and the exceptionally high levels of contamination of certain samples (total mercury contents varied between 0.15 and 3180 mg kg(-1) while total arsenic concentrations ranged from 11 to 6365 mg kg(-1)), the water-soluble percentages of both mercury (<1.2%) and arsenic (<4.6%) were generally low. The variability of the water-soluble fractions of these two elements among these samples and at the occurring pH conditions seems not to be associated with the release of other potentially toxic elements. The highest water-soluble concentrations of the remaining potentially toxic elements were generally observed in the 15-25 cm depth layer of sediments from areas colonised with plants (Halimione portulacoides) and in mining soil samples. Zinc, cobalt, copper and cadmium showed the highest water-soluble percentages of elements in relation to total metal contents. Given the high contamination levels, the availability of potentially toxic elements in these areas as well as possible risks to the environment and humans should be further investigated. The presence of plants (H. portulacoides) appears to cause significant changes in the sediment matrix that increase the mobility of several potentially toxic elements, particularly in the 15-25 cm depth layer. The effects of vegetation on the fractionation of potentially toxic elements on these sediments should be further studied.

Metallothioneins failed to reflect mercury external levels of exposure and bioaccumulation in marine fish – Considerations on tissue and species specific responses

The suitability of metallothioneins (MT) in fish as biomarker of exposure to mercury has been questioned. Therefore, this study aimed at investigating the relationship between external levels of exposure, mercury accumulation and MT content, assessing species and tissue specificities. Two ecologically different fish species--Dicentrarchus labrax and Liza aurata--were surveyed in an estuary historically affected by mercury discharges. Total mercury (T-Hg) and MT content were determined in gills, blood, liver, kidney, muscle and brain. All tissues reflected differences in T-Hg accumulation in both species, although D. labrax accumulated higher levels. Regarding MT, D. labrax revealed a depletion in brain MT content and an incapacity to induce MT synthesis in all the other tissues, whereas L. aurata showed the ability to increase MT in liver and muscle. Tissue-specificities were exhibited in the MT inducing potential and in the susceptibility to MT decrease. L. aurata results presented muscle as the most responsive tissue. None of the investigated tissues displayed significant correlations between T-Hg and MT levels. Overall, the applicability of MT content in fish tissues as biomarker of exposure to mercury was uncertain, reporting limitations in reflecting the metal exposure levels and the subsequent accumulation extent.

Soil–plant–animal transfer models to improve soil protection guidelines: A case study from Portugal

Food chain models are essential tools to assess risks of soil contamination in view of product quality including fodder crops and animal products. Here we link soil to plant transfer (SPT) models for potentially toxic elements (PTEs) including As, Ba, Cd, Co, Cu, Hg, Ni, Pb, Sb, U and Zn with models describing accumulation in animal organs. Current EU standards for food products and acceptable daily intake levels (ADI) for humans were used as critical limits. The combined model is used to assess the impact of soil contamination on animal health, product quality and human health using data from 100 arable fields. Results indicate that 42 existing arable fields near industrial and mining sites are unsuitable for animal grazing in view of food safety due to elevated intake of Cd, Cu, Hg and Pb by cows and sheep. At 10 sites daily intake levels of As by cows exceeded threshold concentrations regarding the quality of animal products. The food chain model also was used inversely to derive soil threshold concentrations in view of EU fodder standards. Calculated threshold levels in soil for As, Cd, Cu, Pb, Hg and Zn appear to be in line with those proposed or used in other EU countries. As such the approach applied here can form a conceptual basis for a more harmonized risk assessment strategy regarding the protection of animal and human health.