S19 Socio-economic factors affecting mercury exposure and risk

By causing the release of natural soil mercury (Hg) towards aquatic environment, the conversion of the Amazon forest into agricultural land has important impacts on ecosystems and human health. As recent studies suggested that soil mercury mobility could result from biomass burning, the implementation of agro-forestry systems could be an interesting alternative to traditional slash-and-burn cultivation to reduce Hg loss. One of the objectives of the PLUPH project is to use Hg human exposure related to environmental change as a lever to promote the adoption of sustainable farming practices, as alternatives to slash-and-burn agriculture, in the Amazon. Rural communities of the Tapajós Region (Brazil) participated in this study. With the collaboration of villagers, three types of agroforestry systems were implemented in 2009. These systems are expected to have a lower negative impact on the environment and on human health, as they may contribute to the diminution of soil erosion and to the retention of soil Hg. Soil samples collected in four agroforestry systems during two sampling campaigns (when they were newly deforested, and after one year of cultivation) showed that a loss of soil Hg occurred at soil surface, suggesting a transfer of the contaminant towards the aquatic environment in the first year of cultivation, which is probably related to the use of fire to clear the forest. Several community workshops were done to discuss the relationships between Hg exposure and agricultural practices. Also, focus groups were realised with different groups of participants in order to better understand local perception and knowledge concerning the relationships between environmental change and human health. Furthermore, semi-directed interviews were conducted in order to investigate farmer’s perceptions about experimenting with agricultural practices that could contribute to enhance Hg retention in agricultural soils. The results showed a marked difference of vision between local communities and researchers regarding their comprehension of the relation between health problems and environmental degradation, and about the possible ways to address the situations. The different visions, as well as the farmer’s perceptions about the benefits and disadvantages of traditional and alternative agriculture, have to be taken into account when implementing projects aiming at addressing human health risks such as Hg exposure, and their relationships with land use practices.

Over the last years our research team has been examining the influence of dietary and nutritional variables on Hg exposure and toxicity in the Brazilian Amazon through interdisciplinary projects. In these riparian populations fish is a nutritious food but it can also be the vehicle of toxic substances such as mercury. Simultaneously, villagers are exposed to other health-promoting foods such as native fruits, which contain a number of phytonutrients that can slow or prevent chronic diseases. Due to the importance of nutritional factors on metals` toxicology, and considering the rich food biodiversity in the Amazon, one of the questions among researchers has been to what extent such food diversity could be used to reduce Hg exposure while maintaining fish consumption. Along those lines, an important scientific finding resulting from a 1-year participatory dietary survey with a group of women reported the ability of native fruit consumption to influence relations between fish consumption and biomarkers of Hg exposure. Further studies have been under way not only to identify nutrients possibly involved with this potential protective effect against Hg exposure, but also to study the feasibility of using the large food biodiversity of this region to reduce such exposure. In the context of the PLUPH project, we have recently determined blood total Hg concentrations, plasma levels of antioxidant vitamins (e.g., vitamins E and A), essential metals (e.g., zinc, copper, manganese, selenium) as well as carotenoids (e.g., lycopene and ß-carotene) in three newly enrolled riparian communities on the Tapajós River, during two seasonal campaigns. As expected, Hg exposure was elevated in both seasons, with higher levels during rainy season (mean: 74 ± 59.1µg/L, range: 7.9 – 231.1) compared to dry season (mean: 37.6 ± 34.7µg/L, range: 1.6 – 178.4). Nutrients were generally found within expected ranges with important seasonal variations, with normal values found for most nutrients during the rainy season (mean vitamin E: 22.1 ± 7.3 µmol/L; mean vitamin A: 1.96 ± 0.44µmol/L; mean zinc: 7933 ± 1945µg/L; mean copper: 846.3 ± 172.8µg/L; mean manganese: 25.2 ± 7.3 µg/L; mean selenium: 358.0 ± 156.1µg/L; mean lycopene: 0.25 ± 0.16 µmol/L; mean ß-carotene: 1.50 ± 1.12 µmol/L), whereas vitamin E and ß-carotene were bellow expected lower limits during the dry season (11.9 ± 3.2 µmol/L and 0.4 ± 0.2 µmol/L, respectively). These data are currently under analyses to examine their possible influence on Hg exposure and biochemical effects on this riparian population.

On the Tapajós River Basin the epidemiological scenario encompassed by the natural formation of soil, deforestation and food intake of the population provides exposure to mercury (Hg). It is known that this exposure has a great potential to trigger different pathological disorders (mainly via oxidative stress). It has been suggested that high blood pressure may be associated with Hg exposure. This study evaluated levels of C-reactive protein, an inflammatory bioindicator of the risk for cardiovascular diseases (CVD), in riparian villagers of the Amazonian Tapajós River by ultrasensitive method (hsCRP), and examined a possible association with total blood Hg (B-Hg), blood pressure (BP), body mass index (BMI), plasma malondialdehyde (MDA), and interleukin 10 (IL-10). The investigation was carried out in three villages: Nova Estrela (NE, n = 36); Araipá-Lago (AL, n = 34) and São Tome (ST, n = 33). B-Hg was analyzed by ICP-MS; plasma MDA by HPLC-UV; serum hsCRP by immunoturbidimetric assay and IL-10 levels using the AlphaLISA Human IL-10. B-Hg levels were significantly lower in NE (11.52 ± 10.30 µg. L^-1) than AL (31.70 ± 22.73 µg. L^-1) and ST (72.01 ± 38.61 µg. L^-1). Globally, the participants of the three communities had BP and BMI within normal ranges. MDA levels were significantly lower in NE (2.05 ± 0.60 µM. L^-1) as compared to AL and NE (7.67 ± 2.50 µM. L^-1 and 6.98 ± 2.88 µM. L^-1, respectively). hsCRP was also lower in the community of NE (0.86 ± 0.67 mg. dL^-1) comparatively to the communities of AL (1.72 ± 0.81 mg. dL^-1) and ST (3.10 ± 0.64 mg. dL^-1). IL-10 levels were significantly different in the three participating communities, being 140.07 ± 41.18 pg. mL^-1; 84.35 ± 38.57 pg. mL^-1 and 61.79 ± 24.53 pg. mL^-1, in NE, AL and ST, respectively. These preliminary results suggest an ongoing inflammatory process in this small population, a low anti-inflammatory response capacity, and the presence of lipid peroxidation in communities presenting higher Hg exposure. Multiple regression analyses are currently under way in order to identify predictors of plasma concentrations of hsCRP in these Hg exposed communities.