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Informal economy of gold mining has contaminated some important river basins in Amazon. Follow-up studies on critical compartments showed some areas with high Hg levels in fish as well as in human hair samples. Average Hg in piscivorous fish in the Madeira river itself was 846 ppb (N=284) with a maximum of 3921 ppb. Mercury in fish from non polluted areas in this basin shows high variability, even for single species. A seasonal variation in Hg content was observed, with higher values at the end of the dry season. In the upper Tapajos basin comparable values were found for fish but with a definite decreasing trend downstream. Average value for piscivorous fish in the whole Tapajos basin is 482 ppb (N=122) with a maximum value of 3770 ppb. Hair Hg was higher in fishing villages in the Tapajos (average: 17 ppm; with N=432 and maximum value of 176 ppm) than in the Madeira (average: 9 ppm; N=169; maximum 71 ppm), and data from some areas of the Tapajos suggest a decrease with time. Mercury was much higher in urine of goldshop workers in Santarem (low Tapajos) than in Alta Floresta (high Tapajos) and show a decreasing trend in both cases, probably related to the significant decline in gold mining activities during the study period (1986-1994).

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.

Mercury is being released in the Amazon in an abusive way due to goldmining activities. The Tapajós river basin was the first to be intensively exploited in the modern Amazon gold rush. Fish and hair samples as the best indicators of human methylmercury contamination were investigated in the main cities and villages along the Tapajós river basin. The upper basin has typical fish fauna with much larger carnivorous fish with higher mercury levels reaching an average value of 0.69 microgram.g-1 wet wt. in 43 fish. This was accompanied by high levels in hair of the human population living in the same area. The maximum hair value reach 151 micrograms.g-1 dry wt. with two villages presenting an average value close to 25 micrograms.g-1 dry wt. An analytical laboratory intercalibration exercise was performed between Japanese and Brazilian laboratories for total mercury analysis. Critical fish, areas, and more exposed human groups are identified.

A field study was conducted in an area of elevated natural background radioactivity (the Pocos de Caldas plateau, Brazil) to assess tissue concentrations and the comparative bioavailability of isotopic Th (IV), U (IV, VI), Ra (II) and light rare earth elements (REE), i.e. La (III) and Ce (III, IV) in adult steers, pigs and chickens. Among animals, analyses are limited primarily to bone and muscle since they represent the major loci for deposition/retention and transport to man, respectively. The assessment of comparative bioavailability was aided by normalizing tissue concentrations to local soil concentrations, i.e. by calculating soil-to-tissue concentration ratios (CRs). Mean CRs (for muscle/soil) in these animals were very similar for U, La and Th which, as a group, decreased among the farm animals sampled as (all × 10 −4 ): chicken (1)/>- steer (0·7) />- pig (0·4). For 226 Ra, CRs in muscle decreased in the same order among animals although mean values were 3–5 times greater than those quoted. Much greater values and greater differences among the elements are noted for bone/soil CRs, which for all animals decreased as: Ra >> U > La = Th , indicating the order of elemental bioavailability (assuming bone to be the major retention compartment). Isotopic ratios in farm animal tissue are shown to resemble closely those in soils over which the animals forage, with few exceptions, indicating the importance of the soil component in the transfer of these elements to tissues.

A field study was conducted in an area of background radioactivity (Orange County, New York) to assess tissue concentrations, soil-to-tissue concentration ratios (CR) and the comparative bioavailability of isotopic Th, U, Ra and light rare earth elements (REE) (i.e. La, Ce, Nd and Sm) in adult steers. The study was undertaken because few field or laboratory data exist on the dietary transfer of these elements to steer tissues and because the elements chosen for study bear many physical, chemical and biological properties which are similar to those of the transuranic actinide elements (i.e. Pu, Am and Cm) contained in high-level nuclear waste. It was shown by analysis of the bovine diet that soil ingestion, occurring incident to grazing, purposefully and/or as surficial contamination on feeds, would under most conditions account for the majority of intake when all possible intake pathways are considered. Exceptions are for the uranium isotopes and 230 Th, which were ingested primarily with a phosphate mineral feed supplement. Because the intakes of most of these elements are dominated by soil ingestion, we have calculated CR values as μg kg −1 (fresh tissue weight) per μg kg −1 (dry soil), as opposed to the more routinely used F ƒ ratio ( F ƒ = μ g kg −1 (fresh muscle weight) per μg day −1 (intake rate from feed)).