Assessing mercury contamiantion in the Amazon

3. Discussion

3.7.2. Fish consumption patterns in the Amazon

Commonly, few fish species represent more than 50% of the fish caught (Castilhos et al., 1998). Catches also show a 1:1 relationship between piscivorous and non-piscivorous species. The same relation is assumed for human consumption. Furthermore, piscivorous fish usually have higher mercury concentrations than omnivorous and herbivorous fish (Table 1).

Tabel 1: Mercury concentrations in pisci-, omni- and herbivorous fish from the Madeira River (Boischio,2000).
Mercury concentrations in fish ( µg/g )
Piscivorous Omnivorous Herbivorous

A survey on fish ingestion rates in ribeirinhos resulted in a median fish ingestion rate of 200g fish per day. Cultural patterns may influence fish consumption patterns (Boischio and Henshel, 2000). Interestingly, local culture defines certain fish to worsen vulnerable stages of life, i.e. illness, pregnancy and breast-feeding. The Aruana fish species is considered the safest fish for consumption and is often consumed during pregnancy and breast-feeding. However, mean mercury concentration for this species is 1.44 µg/g, which is very high (Boischio and Henshel, 2000).
Riverside people of the Amazon, ribeirinhos, also prefer scaled fish rather than non-scaled fish, i.e. catfish (Boischio and Henshel, 2000). In contrast urban populations seem to consume more catfish. Interestingly, scaled fish are generally low in mercury compared to non-scaled fish. The implications are that urban populations are likely to be eating a low amount of fish with high mercury levels, whereas the ribeirinhos are eating large amounts of fish with lower mercury levels. Fish consumption patterns also seem to differ between the dry season and the rainy season. Piscivorous fish are more frequently consumed in the wet season, while herbivorous and omnivorous fish are more frequently consumed in the dry season (Lebel et al., 1997). This is reflected in higher hair mercury concentrations in humans in the rainy season, when compared to the dry season (Lebel et al., 1997).

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