Background

Human actions derived from industrial activities, agriculture and domestic sewage are among those responsible for the pollution of the environment by toxic metals (Biondo, 2008). Mercury occurs in the environment combined with other elements and naturally in different chemical species with distinct solubility, reactivity and toxicity. Occurring in volcanoes and mercury mines, which are responsible for emissions of mercury in the order of 2700-6000 tons/year (Micaroni et al. 2000). In the Amazon, it is also used in mines in the amalgamation of gold (Au-Hg) (Figura 1), where a quantity of metallic mercury (Hg0) is released upon rivers and soils by the handling in insecure situations, and through the outdoor burning process, which releases element's vapor to the atmosphere, that leads to the aquatic ecosystem contamination.

Figure 1. Direct contact with mercury in the Amalgamation of gold process.

In Amazon rivers, about 3000 tons of mercury are available and can be bioconverted in its most toxic forms for living beings, through methylation - the addition of the radical CH3 – of mercury, bioaccumulative properties are acquired by its high affinity to animal tissues (Souza and Barbosa, 2010). The mercury methylation is a crucial step to its entry in the aquatic food chain organisms, because of it riverside communitiesA traditional pupulation that resides in the rivers proximities and they have the artisanal fishing as main food supplying activity. are the main affected by contaminated fish ingestion.

Figure 2. Death of fish caused by dumping Mercury in the river.

Worldwide, there are cases of accidents with mercury as occurred in 1908 with the chemical industry Chisso Corporation that produced fertilizers settled in Minamata Bay in Japan. In 1932 the factory started to produce acetaldehyde, mercury sulfate in production, reaching 6,000 tons in 1951 and 42,245 tons in 1960.

Chisso's factory did not properly dispose their liquid waste, which were released into Minamata Bay since 1946, being continuously disposed residue, eventually affect sea Shiranui and others around it. In April 1956 the first signs of poisoning in people and changes in the ecosystem of the bay were observed. After humans and cats had the same symptoms and marine creatures are constantly found dead, the condition was named Minamata disease. The level of mercury contamination of the Minamata disease patients in the 50`s, reaching up to 705 ppm.

The second major accident is recorded in Iraq (1972), where epidemic proportions of mercury contamination were observed after wheat seeds were treated with alkyl mercury and were inappropriately consumed as food. It is not known how long it takes to develop symptoms of mercury poisoning or not, Because it is directly dependent on the form, concentration and time of exposure to the metal. After these accidents occurred, conventions and legislation in countries were determined individually, in addition, this type of action demonstrates the awareness and concern by government part.