Use of chitosan in the adsorption of metals in sediments from contaminated streams: bioremediation of impacted areas and effects on Chironomus xanthus larvae

Abstract

The State of São Paulo leads the list of sugarcane cultivation, destined for sugar and ethanol production, with 4.515.360 hectares of cultived area. However, the use of herbicides and fertilizers during the different stages of sugarcane cultivation causes stream metals contamination such as copper , lead, chromium , nickel, manganese , magnesium , zinc and cádmium elements. In this areas we also have an intense riparian vegetation degradation, which collaborates in impacts in adjacent areas of these plantations, resulting in loss of biodiversity. Consequently , the condition of the local biota becomes a good indicator of the integrity of an aquatic environment around this plantation. In order to understand the environment impacts, detailed studies will be conducted , using aquatic insect larvae (Chironomus xanthus ), to evaluate the processes of contamination and bioaccumulation of metals in these organisms . The high concentration of non-essential metals to organisms can cause changes in the life cycle of certain species of aquatic insects as Chironomus xanthus. Chitosan is an abundant biopolymer obtained from chitin, which occurs in exoskeletons of crustaceans, such as shrimp shells and crab shells. Chitosan provides great opportunities in various cientific fields (as medical, pharmaceutical, cosmetics , food, textile and environmental). Being a renewable resource and possess excellent properties , chitosan has been used as flocculant in wastewater treatment of various situations. The presence of 2-amino- 2-deoxy -D- glucopyranose units, which contains the amine group in its composition, provides a cationic character of chitosan in an acid environment that is responsible for flocculating capability and also by the adsorption of metals ions. Chitosan will be firstly used in toxicity tests with larvae of Chironomus xanthus and then will be used in the presence of metals found in the sediments of contaminated streams in order to analise the possible sequester metal ions from sediments by chitosan. Consequently, the present study can contribute to reduce the impacts of metals from sugar-cane cultivation to aquatic biota and to stream environment. These data may contribute as basis for new strategies for restoration with sugarcane cultivation areas, without riparian vegetation. (AU)