Manganese: a new Emerging Contaminant in the Environment.

The environment is composed of the atmosphere, earth and water. According to the World Health Organization, more than 100,000 chemicals are released into the global ambient every year as a consequence oftheir production, use and disposal. The fate of a chemical substance depends on its chemical application and physical-chemical properties, in combination with the characteristics of the environment where it is released. Chemical substances or contaminants discharged intothe environment may be "natural" or "manmade". One of the most misunderstood concepts regarding contamination is the missinterpretation of term "natural". A "natural" contaminant is one substance that can occur without human introduction. For example, trace metals, suchas iron, zinc, manganese, copper, cobalt and nickel, can be considered naturally-occurring contaminants. Generally, these metals are found in the environment only in moderate amounts that do not cause health threats. However, "natural" contaminants can also have anthropogenic origins: in fact human activities often cause the release of a large amount of naturally-occurring minerals into the environment. Moreover, it isnot the mere presence of a contaminant that makes it toxic, but its concentration. Paracelsus' famous aphorism "only dose makes the difference" has laid the groundwork for the development of the modern toxicology by recognizing the importance of the dose-response relationship. In the last century, the massive production of manganese-containing compounds (metallurgic and chemical products, municipal wastewater discharges, sewage sludge, alloys, steel, iron, ceramics, fungicide products) has attracted the attention of scientists who investigated manganese as a potential emerging contaminant in the environment, and especially in the marine environment (CICAD 63, 2004). In humans, manganese excess is renowned for its role in neurotoxicity, associated with a characteristic syndrome called 'manganese madness' or 'Parkinson-like' diseases (Perl & Olanow, 2007). This neurodegenerative disorder is due to the accumulation of manganese inside intracellular compartments, such as the Golgi apparatus and mitochondria. In mammals, prenatal and postnatal exposure to manganese is associatedwith embryo-toxicity, fetal-toxicity, and decreased postnatal growth(Sanchez et al., 1993; Colomina et al., 1996). In marine organisms some studied showed that an excessive amount of manganese causes toxicity, although the cause-effect evidence is not extensive. In this chapter, we will provide: firstly the information available regarding the natural behaviour of manganese in the environment and its role in the living organisms, with particular emphasis on the marine environment. Secondly, we will discuss how and why the manganese contamination has become a global problem recently. Thirdly, we will cover some aspects regarding the adverse effects resulting from the exposure of whole organisms to high levels of manganese.Advantage of the notion that marine invertebrates express qualitatively similar types of induced damage tothose found in higher organisms, we will focus our attention on the toxicity of manganese at different levels of organization: wholeorganism, cellular and embryonic levels. In thisreview chapter we intend to promote the embryos and the immune cells of echinoderms as useful models to study manganese toxicity.