Screening-level integration of human health and ecological risk assessment of metal(loid)s in surface water severely affected by landfill and agricultural activities in Ayutthaya landfill, Thailand

This study aimed to evaluate contamination levels, potential sources, and associated ecological and human health risks of metal(loid)s in surface water surrounding a municipal solid waste landfill and adjacent agricultural areas under a worst-case exposure scenario. The results indicated that during the pre-monsoon season, mean metal(loid) concentrations followed the order manganese > iron > copper > arsenic > nickel > lead > cadmium, whereas during the monsoon season the order was iron > manganese > nickel > arsenic > copper > lead > cadmium. Notably, arsenic concentrations in both seasons and manganese concentrations during the monsoon season exceeded Thai surface water quality standards for domestic and human use, as well as the Australian Drinking Water Guidelines. Source apportionment analysis identified contributions from landfill leachate, agricultural activities, and naturally occurring geochemical sources. Screening-level ecological risk assessment under a worst-case exposure scenario revealed that all metal(loid)s, except Pb, in both the pre-monsoon and monsoon seasons exceeded the threshold for adverse ecological effects. Screening-level human health risk assessment under a worst-case exposure scenario indicated cumulative non-carcinogenic and carcinogenic risks associated with multi-element exposure for both children and adults across both seasons, resulting from exceedances of health risk–based screening benchmarks when long-term exposure to season-specific concentrations was assumed. These findings highlight screening-level concerns for populations relying on surface water resources and underscore the need for further site-specific investigations and improved management of agrochemical use and municipal solid waste landfills to protect surface water quality.