Micropollutant Degradation Mechanism

Abstract

The organic pollution is a major concern during the treatment of drinking-water as organic micro-pollutants might show disruptive and toxic properties. Organic micro-pollutants are found in surface and groundwaters at different concentrations, mostly between 0,1 and 100 μg/L (Panno&Kelly, 2004). Pesticides are known contaminants of concern. 363 kt of pesticides were used between 1980 and 1990 in the USA. From among triazine pesticides, atrazine and its metabolites, deethylatrazine and deisopropylatrazine, can still be found in drinking-water supplies throughout the EU, due to their usage as maize and sugar beet pesticide. They are slowly biodegradable microbiologically (Reid et al, 2003). They have to be removed from drinkingwater sources because they are classified as possible human carcinogens (Legube et al, 2004). Atrazine, with the chemical name 2-chloro-4-(ethylamino)-6-(isopropylamino)-striazine (C8H14ClN5, MCIET = 215,7 g/mol) is soluble in water at 30 mg/L and half live in soil for atrazine is 15−100 days (Ralebitso et al, 2002). Atrazine is classified as a class C carcinogen. Chromosom damage to chinese hamster egg cells were observed if they were exposed to 0,005−0,080 μmol/L of atrazine, within two days. Two well-known atrazine metabolites, deethylatrazine and deisopropylatrazine, were found to be potentially carcinogenic, therefore the admissible levels for each pesticide individually in water are set at 0,1 ug/L, and the sum should not exceed 0,5 μg/L in EU (Thurman et. al, 1994). US EPA (US Environmental Protection Agency) set the total admissible levels for atrazine, deethylatrazine and deisopropylatrazine in groundwater at 3 μg/L (Richards et al, 1995). A study by US EPA in 2003 showed that triazines – atrazine, simazine and propazine – as well as metabolites – deethylatrazine and deisopropylatrazine in deethyldeisopropylatrazine – have the same mechanism concerning endocrine disruptions. Anumnerated compounds act the same way on human bodies, therefore, US EPA introduced the sum of all chloro−s−triazines. Atrazine removal from drinking water sources is impossible using chlorination, aeration, filtration or coagulation. Quite effective technologies include activated carbon, ozonation, membrane separatoin, and biofiltration. The most efective are RO and NF membranes (Jiang&Adams, 2006). During a study of atrazine degradation within concentrations ranging from 5 to 1700 ng/L, the only metabolite found was deethylatrazine within a concentration range from 10−850 ng/L (Garmouna et al., 1997).