Estudo dos riscos à saúde humana associados com a exposição a trihalometanos e ácidos haloacéticos presentes nas águas tratadas de ETAS que abastecem a cidade de Salvador-Bahia.

Abstract

In water treatment plants (WTPs), during the oxidation and disinfection stages involving chlorine, secondary reactions usually occur with natural and anthropogenic organic matter, generating disinfection byproducts (DBPs). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the most extensively investigated DBPs in drinking water due to the toxicity and adverse effects on human health. This study aimed to assess the human health risks associated with exposure to THMs and HAAs in drinking water from WTPs supplying the population of Salvador, Bahia, during the period from 2019 to 2022. Deterministic and probabilistic analysis were used to calculate and evaluate lifetime carcinogenic risks (LCR) and non-carcinogenic risks (as HQ or HI) through ingestion and dermal absorption, considering 3 age groups (0– 5, 6–19, and 20–70 years, referred to as G1, G2, and G3, respectively). Overall, 60% of the mean concentrations of total THMs and 62.5% of total HAAs exceeded the maximum limits of 80 μg L-1 and 60 μg L-1, respectively, established by the USEPA. Additionally, approximately 50% of the THM exceeded the limit (100 μg L-1) established by the WHO and Brazilian regulations. The results obtained by the deterministic risk assessment (DRA) indicated that for all age groups, the ingestion route was the one that presented the highest LCR values. For THMs 100% of the LCR values by ingestion for the compounds TCM, BDCM and DBCM exceeded the lower acceptable limit established by the USEPA (1.0x10-6). Regarding HAAs, 100% of the values for dichloroacetic acid (DCAA) and 97% for trichloroacetic acid (TCAA) also exceeded this limit. Despite lower risks, dermal absorption remained relevant, particularly for TCM. According to probabilistic risk assessment (PRA) using Monte Carlo simulation, all LCR values in the 95th percentile (estimate of the upper limit of potential risk) for the 3 THMs and 2 HAAs evaluated exceeded the lower acceptable limit to the USEPA for all age groups by ingestion route. Considering the highest limit (1.0x10-5) set by the WHO, 74% and 89% of the LCR values in this percentile associated with THMs and HAAs, respectively, exceeded this limit by this exposure route, therefore indicating high carcinogenic risk to the exposed population. Although the HQ values for the 3 THMs and TCAA were below the USEPA limit (HQ < 1), DCAA in ETA1 and ETA2 showed HQ > 1 for children (G1) at the 95th percentile. Moreover, 25% of the HI values for THMs and 67% for HAAs exceeded the acceptable limit, indicating significant non-carcinogenic risks. Sensitivity analysis revealed that concentration and BW were the most influential variables contributing to risk in most of the evaluated groups. PCA indicated that chlorine dose in prechlorination is the main variable associated with the formation of THMs and HAAs, showing positive correlations with water quality parameters such as DOC, temperature, and pH. HCA grouped the variables into two distinct clusters: one to DBPs formation and other to final disinfection. LDA, based on precipitation data, achieved 95.83% classification accuracy, distinguishing samples from different WTPs. The results showed the need for measures to reduce the formation and risks of these DBPs, ensure water quality, and protect the health of Salvador's population.