Passive sampler-based pathway monitoring of melamine-series contaminants and triazine herbicides in an urban tributary.

The environmental occurrence of melamine deamination series and triazine herbicides represents a significant challenge for aquatic monitoring due to their high mobility and persistence. This study investigated cyromazine, melamine, its deamination products, and selected triazine herbicides in an urban tributary using two passive samplers, the Polar Organic Chemical Integrative Sampler (POCIS) and the Chemcatcher. Four 14-day monitoring campaigns were conducted, and passive sampler-derived time-weighted average concentrations were used to evaluate contaminant occurrence, environmental transformation, sampler comparability, and screening-level ecological risk. Melamine and cyromazine were frequently detected, indicating recurrent inputs of parent melamine-series compounds. Ammeline, ammelide, and cyanuric acid were also detected across several site-periods, demonstrating that transformation products can contribute substantially to the total triazine-related burden. Atrazine and cyanazine occurred only during the spring campaign, suggesting episodic herbicide inputs, whereas simazine was detected more persistently at lower concentrations. Molar diagnostic indices indicated that melamine-series dominated the triazine-related burden. POCIS and Chemcatcher yielded comparable detection patterns, although POCIS generally showed higher responses for the highly polar melamine-series compounds. The screening-level mixture risk was governed by atrazine during spring; When atrazine was excluded, the mixture risk quotients remained below 1. Overall, this study supports passive sampler-based pathway monitoring as a useful approach for persistent, mobile, toxic (PMT)-relevant melamine-series contaminants and highlights the need to include intermediate transformation products in water-quality surveillance and screening-level risk assessment.