Avaliação do risco à saúde humana pela exposição aos subprodutos da cloração da água do sistema de abastecimento público

Abstract

Due to the population growth and quality loss of the water sources for public supply, it has becoming even more challenging to supply populations with water of ideal quality and quantity, through the conventional water treatment technologies. Water filtration and desinfection processes are fundamental technologies used for human supply waters. Nevertheless, these technologies may generate residues or chlorination by-products which cause risks to the population health. Due to this serious concern, this thesis has as main objective to evaluate the efficiency of the drinking water treatment of the distribution system. This research also studied the sanitary risks linked to the chlorination by-products generation. Initially, a systematic review upon the trihalomethanes (THM) toxicological aspects was made. These THM are generated in the public supply water desinfection by the chlorination process, that identified the need for deeper studies which seek for evaluate the conditions of population exposition to this toxic substances family, once it present potential to induce cytotoxic and genotoxic to different organisms, human included. This review led the following steps for the risk evaluation proposed by this thesis. In this sense, water samples were collected in a water treatment plant (WTP), located at Extremoz City - Rio Grande do Norte State (RN), which supplies part of the northern Natal City, aiming at the identification of processes linked to the THM formations, also considering the sanitary risks evaluation front of these chlorination by-products exposure. Analyses results demonstrated that THM formation is related to the chlorination conditions, such as contact time and concentration, raw water characteristics - such as concentration and organic matter properties. In addition, filter washing water (FWW) which was treated in sedimentation pond and then recirculated in the system contributes to the generation of cyanobacteria which, in turn, are potentially cyanotoxin producers, originating one more possible source of population health risk. The risk assessment showed that the WTP treated water - consumed by the population has a non-carcinogenic risk 8 to 9 times higher than the permitted level (Hazard Index greater than 1 affects the human health). On the other hand, the carcinogenic risk (CR) was found to be 400 to 500 times greater than the allowed (CR = 470x10- 5 ), and the highest concentration of chloroform in inhalation and oral exposure are the main risk factors for THM. In this scenary, this study concludes that public supplied water, characterized by its high organic matter content, which is treated by direct filtration, FWW recirculation and disinfection, presents non-carcinogenic and carcinogenic sanitary risks due to the high formation of THM. Therefore, it is evident that the type of WTP's operation for treating high content organic matter raw water generates health risks to populations, which involves around 160 thousands of residences. Indeed, in view of this scenario, new strategies of water treatments that reduce the chlorination by-products and cyanotoxins in order to avoid the induction of cancer and other to health risks to human populations are proposed, such as modification of the used disinfectant, reduced sedimentation pond´s retention time and a post-treatment with activated carbon filter.