Jean Remy Davée Guimarães

Effects of Recent Human Colonization on the Presence of Mercury in Amazonian Ecosystems

Three Hg sources were characterised and mass balance calculations were used to determine their relative contributions to the contamination of the Amazonian environment. About an order of magnitude more Hg is emitted to the atmosphere by goldmining activity than by the burning of forest biomass. However, anthropogenic atmospheric Hg cannot account for the high Hg burdens found in terrestrial ecosystems: deposition of Hg from goldmining sources is estimated to account for less than 3% of the Hg present in the surface horizons of soils. We propose that erosion of deforested soils following human colonization constitutes a major disturbance of the natural Hg cycle. Deforestation thus increases soil Hg mobilisation by runoff, which may explain the increase of Hg burdens in Amazonian aquatic ecosystems in newly colonized watersheds.

The geochemistry of mercury in central Amazonian soils developed on the Alter-do-Chão formation of the lower Tapajós River Valley, Pará state, Brazil.

In an oxisol-spodosol system developed on the terrestrial surface of the lower Tapajós Valley, the determination of total mercury (Hg), organic carbon (C), iron and aluminum oxy-hydroxide (Fe(cdb) and Al(cdb)) concentrations in the surface soil horizons are used to characterise the geochemical processes controlling the accumulation of Hg in soils under natural vegetation cover and in deforested and cultivated sites. Oxisols from the plateau have homogeneous and relatively high background Hg contents and burdens constituting an important natural reservoir of Hg for the region (90-210 ng/g dry wt. and 19-33 mg/m2 for the first 20 cm). The Fe(cdb) and Al(cdb) contents associated with the fine fraction (< 63 microns) of the soil suggest that oxy-hydroxides and, particularly Al-substituted Fe oxy-hydroxides, control the Hg concentrations observed in all of the soils of the study region. Consequently, the geochemistry of these minerals along the slopes governs the accumulation or the release of the Hg according to the natural evolution of the soil cover and/or following the degradation of soils by erosion after deforestation and cultivation. These observations have important implications for the interpretation of Hg contamination patterns observed in Amazonian aquatic systems that could be linked to different drainage sources of Hg from the terrestrial surface. The sandification and podzolisation that is characteristic of the evolution of numerous pedological systems in the equatorial Amazon could be responsible for exportation of the naturally accumulated Hg, as for other metals, by acidic complexation and migration to the black waters of the Amazon. In the central Amazon region, as a result of the fragility of the soil cover, deforestation and cultivation, affecting principally the superficial soil, promote the selective erosion of fine particles enriched in oxides and Hg. The erosion of soil could be responsible for an important release of Hg, transported in particulate form by drainage waters.

Human Exposure to Mercury Due to Goldmining in the Tapajos River Basin, Amazon, Brazil: Speciation of Mercury in Human Hair, Blood and Urine

To obtain the basic information on human exposure to mercury (Hg) due to gold mining activities in Amazon, total mercury (T-Hg) and methylmereury ~,MeI Ig) were determined for human hair, blood and/or urine samples collected from populations living in gold mining area and fishing villages upstream of the Tapajos River basin. Abnormally high levels of T-Hg were observed in hair and blood from all fishing villages investigated and more than 90% of T-Hg was in the form of MeHg in both samples, whereas in goldmining area the value were much lower and the %MeHg value~ varied widely (20-100~ with individuals even in blood samples. Urine from gold shop workers contained Hg mostly in inorganic lbrm at 165 tLg/g creatinine on the average, with the range of 20 to 450 tlg/g creatinine. A good correlation between tlg in hair and blood was fotmd in fishing villages and the ratios of hair Hg to blood Hg were very close to 250, generally established for MeItg. T-IIg and inorganic Hg levels in urine from gold shop workers were also signilicantly correlated with inorganic Hg in blood. 1.Introduction Environmental mercury (Hg) pollution due to gold mining in theAmazonian region has become a m a t t e r o f worldwide concern in recent years. In the goldmining processes an enormous amount o f metallic Hg has been used and released in an abusive way into local ecosystems over the last 20 years. It is estimated that around 100 tons of Hg have been released annually, o f which 45% are discharged into river systems and 55% into the atmosphere (Preiffer and Lacerda, 1988). Owing to this metal, therefore, there i s a possibility of causing two types of health hazards in the Amazon river basin: First, occupational inorganic Hg poisoning by direct inhalation of r ig vapor during the processes of burning and re-burning Hg-Au amalgam. Secondly, a part o f Hg discharged into river systems is methylated and ultimately bio-accumulated to a significant level in fish. Thus, people living along the fiver and depending on riverine products are easily exposed to MeHg and may develop toxic levels through repeated consumption of these contaminated fish. The people living near gold mining areas may be contaminated with at least two forms of Hg inorganic Hg and MeHg simtlltaneously from surrounding air and diets. Though, in fact, high levels o f Hg in hair and fish from the main tributaries of Amazon river have Water, Air, and Soil Pollution 80: 85-94, 1995. 9 1995 Kluwer Academic Publishers. Printed in the Netherlands.

Mercury net methylation in five tropical flood plain regions of Brazil: high in the root zone of floating macrophyte mats but low in surface sediments and flooded soils.

Mercury net methylation in five tropical flood plain regions of Brazil: high in the root zone of floating macrophyte mats, but low in surface sediments and flooded soils

Mercury fluxes in a natural forested Amazonian catchment (Serra do Navio, Amapá State, Brazil).

Mercury (Hg total) fluxes were calculated for rainwater, throughfall and stream water in a small catchment located in the northeastern region of the Brazilian Amazon (Serra do Navio, Amapá State), whose upper part is covered by a natural rainforest and lower part was altered due to deforestation and activities related to manganese mining. The catchment area is 200 km from the nearest gold mining (garimpo). Minimum and maximum Hg concentrations were measured monthly from October 1996 to September 1997 and were 3.5-23.4 ng l(-1) for rainwater, 16.5-82.7 ng l(-1) for throughfall (March-August 1997) and 1.2-6.1 and 4.2-18.8 ng l(-1) for stream water, in natural and disturbed areas, respectively. In the natural area, the inputs were 18.2 microg m 2 year(-1) in rainwater and 72 microg m(-2) year(-1) in throughfall. This enrichment was attributed to dry deposition. The stream output of 2.9 microg m(-2) year(-1) indicates that Hg is being recycled within the forest as other chemical species or is being retained by the soil system, as confirmed by the cumulative Hg burden in the 0-10 cm surface layer, which was 36480 microg m(-2). When the disturbed area of the catchment was included, the stream output was 9.3 microg m(-2), clearly indicating the impact of the deforestation of the lower part of the basin on the release of mercury. The Hg burden in the disturbed area was 7560 microg m(-2) for the 0-10 cm surface layer.

Methylmercury in water, seston, and epiphyton of an Amazonian river and its floodplain, Tapajós River, Brazil.

Levels and accumulation of MeHg were characterized in filtered water, suspended organo-mineral matter, phytoplankton, zooplankton and epiphyton during the dry season and the wet season. In open water of the lentic and lotic ecosystems, the MeHg in filtered water (< 0.2 microm) was near or below the detection limit (< 0.02-0.03 ng/l). These concentrations represent < 5% of the Hgtot. content in filtered water. Inundated forests (Igapó) and macrophyte floating mats were the only sites where MeHg was significantly detected (0.07-0.24 ng/l), representing 3-22% of the Hgtot. in filtered water. MeHg concentrations in organo-mineral suspended matter (2-26 ng/g dry wt. representing 0.6-7.3% of Hgtot.) were correlated with the N content but not with the C content. Data suggest that MeHg enrichment of suspended matter is strongly influenced by the presence of degraded planktonic remains relatively rich in N and MeHg. In zooplankton, MeHg concentrations (20-140 ng/g dry wt.) increased from the dry season to the end of the wet season. This increase was followed by higher proportions of MeHg during the wet season in comparison to the dry season (15-40 to 50-70% of the Hgtot.). The epiphytic material collected from the roots of macrophyte floating mats contained 2-8.5 ng/g dry wt. of MeHg. The proportion of MeHg to Hgtot. in epiphyton (1.5-8.3%) correlated with its C and N contents. The data suggest a greater bioavailability of MeHg in the Tapaj6s River ecosystems due to the seasonal increase in water level and the consequent inundation of the floodplain. Inundation favours the development of large macrophyte floating mats which increases the bioavailability of epiphyton to herbivorous/detritivorous fish. The root zone of floating macrophytes and the flooded organic horizon of the Igapó forest are the only sites along the Tapajós River where significant MeHg can be detected in the water column and sediment. This new study supports the hypothesis that MeHg production and transfer to the first link of the food chain in Amazonian river systems is closely related to organic matter biogeochemistry in the floodplain environment.

Hg methylation in sediments and floating meadows of a tropical lake in the Pantanal floodplain, Brazil

Potential net 203Hg methylation was assayed in different substrates and conditions in Fazenda Ipiranga Lake, 30 km downstream from gold mining fields near Pocone, Pantanal, Brazil, during the dry season. Samples and acidified controls of surface sediments and roots of dominant floating macrophytes (Eichhornia azurea, Salvinia sp.) were incubated in situ for 3 days with approx. 43 ng Hg.g−1 (dry weight), added as 203HgCl2. Methylmercury (Me203Hg) was extracted in toluene and measured by beta counting. Net methylation was about 1% in sediments under floating macrophytes, both at an open lake site and at a littoral site. Parallel incubations of sulphate or molybdate amended samples suggest that sulphate reducing bacteria may be important Hg methylators at both sites, and that their activity is sulphate-limited in particular at the littoral site. In laboratory experiments, net methylation in the same sediments was highest at temperatures in the 33–45°C range but was completely inhibited at 55°C. NaCl addition had a strong inhibiting effect on net methylation. In an intact open-lake sediment core, spiked with 203Hg in the overlying water and incubated for 3 days, total 203Hg was detectable down to a depth of 14–16 cm, coinciding with the depth reached by the galleries of chironomid larvae present in the core. Swimming insects caused 203Hg penetration down to 4 cm. Me203Hg was detected only in the upper layers (0–2 cm) of the sediment, with concentrations reaching 0.47–0.75% of total Hg. This suggests an important role for bioturbation in the exchange of Hg and MeHg between sediment and water. Methylation was up to nine times more intense in floating macrophyte roots than in the underlying surface sediments: an average of 10.4% of added Hg was methylated in samples of Salvinia sp. roots during the 3-day incubation, and 6.5% in E. azurea roots. This adds to previous findings on the role of such macrophyte stands, a distinctive feature of tropical rivers and lakes, as potentially important sites for the production of highly available MeHg.

An assessment of Hg pollution in different goldmining areas, Amazon Brazil

Abstract Metallic mercury used in gold prospecting is being dispersed over Amazon ecosystems through atmospheric emissions as well as directly to aquatic systems. Total mercury concentrations in the more representative environmental (air, soil, bottom sediments, fishes and plants) and human (hair and urine) indicators, collected in the last 7 years in different goldmining areas (garimpos) are presented and discussed. Critical exposure situations, pathways, areas and human groups are indicated. The goldminers (garimpeiros) that manipulate a major part of the Hg are not the critical group either from exposure to metallic mercury (Hg0) by inhalation or exposure to methylmercury by ingestion of contaminated fish. Results obtained from air and urine sampling show that people working in gold dealers shops are the critical group concerning Hg0 risk, while riverine communities are the risk group with respect to methylmercury.

METHYLMERCURY PRODUCTION AND ACCUMULATION IN SEDIMENTS AND SOILS OF AN AMAZONIAN FLOODPLAIN - EFFECT OF SEASONAL INUNDATION ?

This study investigated the spatialand seasonal variations of MeHg concentrations andburdens of different sediments and soils of theTapajós river floodplain, one of the majorclear-water tributaries of the Amazon. The smallfloodplain of the Tapajós is typical of Amazonianfloodplain ecosystems. The studied lakes are borderedby inundated forest (igapó), while floatingmacrophyte mats (Paspalum sp.) develop at themargin of lakes during the flooded season. During theflood, we observed very low MeHg concentrations in theopen water lake sediments (<0.5 ng g-1 d.w or<0.5 μg m-2 cm-1 d.w.) as compared to thesemi-aquatic sediments of the macrophyte zone (0.2–1.4 ng g-1 d.w or 1–3 μg m-2cm-1 d.w.) and the igapó semi-terrestrial soils (0.2–3 ng g-1 d.w or2–12 μg m-2 cm-1 d.w.). The litter horizon fromthe igapó soils showed the highest value of MeHg(4–8 ng g-1 d.w.) representing 0.2–2 μg m-2cm-1 d.w. at the sediment/water interface during theaquatic phase. The inundation had no effect on theconcentrations and burdens of MeHg in the sediment ofthe central part of the lake. The inundation had aclear effect on the methylation of Hg at the surfaceof semi-aquatic shoreline sediments (macrophyte zone)and semi-terrestrial forest soils, where MeHgconcentrations and burdens appeared to be 3 timesgreater following inundation. In all cores, total Hgconcentrations follow those of Fe and Aloxy-hydroxides, whereas the MeHg concentrations arelinked to organic matter quality and quantity. It issuggested that organic matter and inundation controlMeHg production and accumulation at the benthicinterface. These results confirm previousobservations, in the same study area, of net203Hg methylation potentials. The fresh andlabile organic matter in the litter of the igapóforest appears as the most important factor leading tosignificant enrichment of MeHg in these particularterrestrial/aquatic sedimentary environments.

Daily mercury intake in fish-eating populations in the Brazilian Amazon

Although high levels of fish consumption and bioindicators of mercury exposure have been reported for traditional populations in the Amazon, little is known about their actual daily intake of Hg. Using an ecosystem approach, calculate daily mercury intake in adult fish-eaters, examine the relations between mercury intake and bioindicators of exposure and the factors that influence these relations. A cross-sectional dietary survey on fish and fruit consumption frequency was carried out with 256 persons from six villages of the Tapajós River. Fish portion per meal was determined. Mercury concentration was determined for 1123 local fish specimens. Daily mercury intake (μg/kg/day) was determined for men and women from each village using the average fish-mercury concentration for the fish caught in their fishing zone, the average quantity of fish per meal, fish-species frequency consumption and participants’ body weight. Fish-mercury averaged 0.33 μg/g±0.33. Daily mercury intake varied between 0 and 11.8 μg/kg/day (mean 0.92 μg/kg/day±0.89) and varied by gender and village. Mean blood- and hair-mercury were 58.7±36.1 μg/l and 17.9±11.5 μg/g, respectively. There was a strong and positive relation between blood-mercury and daily mercury intake, with an inverse relation for fruit intake and schooling; significant variations were observed with immigrant status, and among villages. Hair-mercury was directly associated with daily mercury intake and inversely related to schooling and fruit consumption. Fruit consumption modified the relation between daily mercury intake and blood-mercury levels: for the same daily mercury intake, persons eating more fruit had lower blood-mercury concentrations (ANCOVA Interaction term: F=10.9, P<0.0001). The median difference of the ratio of blood-mercury to daily mercury intake between low and high fruit consumers was 26, representing a 26.3% reduction. These findings reveal high levels of daily mercury intake. Rigorous studies for developing risk-based reference doses in the Amazon should be undertaken to orient viable risk-management strategies to reduce exposure, while maintaining fish diet.