Health risk assessment of arsenic and lead and their spatial distribution in groundwater at Ban Khai District, Rayong Province, Thailand

Arsenic (As) and lead (Pb) contamination in groundwater is an important public health concern. This study is aimed at i) investigating As speciation and Pb levels between the dry season (March 2019) and the wet season (August 2019) and includes the spatial distribution in groundwater for the purpose of ii) determining the association between the two metals and the hydrochemical parameters. iii) The presence of heavy metals in the urine of 110 participants was evaluated by comparing those persons who had consumed groundwater from a well with As below 10 µg/L (L group) with those who had consumed water with levels above 10 µg/L (H group). Information from face-to-face interviewing was used to explain the factors relevant to iv) a health risk assessment of these participants. This assessment consisted of two methods, namely, a deterministic of the As species and a probabilistic of As and Pb.The As level in the Ban Khai district area ranged from <0.300 to 183.00 µg/L, accounting for 22% of forty groundwater wells, which is above the guideline value of 10 µg/L set by the WHO. The predominant species showed a pentavalent form that had been influenced by oxidation conditions and pH level (6 to 8). Meanwhile, the Pb concentration in the whole area was found to be below the WHO guideline of 10 µg/L. However, the spatial distribution of the two metals was not different in the two seasons. The As case can be explained by the effect of the groundwater flow that spent time mobilizing, while the Pb case can be described by its concentration and behavior. The primary sources of As and Pb may have originated from the weathering of minerals; while in some hot-spot wells, the presence of As might have been the result of anthropogenic activities in the nearby area.Nearly 98% of the samples showed that the presence of Pb in the urine was within the normal level of 60 µg/gCr, as established by the National Institute of Occupational Safety and Health. While the As level in the urine ranged from 5.38 to 600.86 µg/L, the levels in approximately one-third of the samples exceeded the normal level of 50 µg/L that had been set by the National Health and Nutrition Examination Survey. The groundwater consumption from the well which had high levels of As was strongly related to the As levels in the urine of participants in the H group. Meanwhile, the socio-demographic factors of these residents had no association with differences in UAs levels between the L and H groups. The health risk assessment of As species showed that the area had the predominant forms of HAsO4-2 and H2AsO4-, followed by H3AsO3, respectively. For probabilistic risks, drinking water was a major route for both non-cancer and cancer risks. The sensitivity analysis reported that As concentration had the highest impact on changes to the health risk value. Therefore, the local residents who had high UAs level should primarily monitor their health effects to protect against any long-term health consequences, especially cancer development. Meanwhile, an alternative source of water and an effective household treatment, in particular, was recommended, along with a specific method for decreasing As(V) levels prior to drinking.