Contaminant distribution and migration in roofing rainwater: Implications for sustainable utilization and pollution control

Abstract

Understanding contaminant distribution and migration characteristics is crucial for the sustainable utilization of roofing rainwater resources, given the impacts of rapid urbanization and climate change. This study undertook the monitoring of 15 typical rainfall events in Xi'an, China, to analyze the distribution and migration of organic matter, nitrogen, and typical emerging contaminants (ECs) during wet deposition (WD), roofing erosion, and roof runoff (RR). The results indicate the concentration levels of organic matter, and nitrogen as follows: COD, 22.69 ± 1.52–132.83 ± 3.43 mg/L; TOC, 3.45 ± 0.22–27.64 ± 1.12 mg/L; TON, 4.99 ± 0.28–12.38 ± 1.55 mg/L; DTN, 4.54 ± 0.10–11.87 ± 0.83 mg/L; PTN, 1.32 ± 0.14–6.57 ± 0.40 mg/L. Additionally, specific emerging contaminants were found at the following concentrations: endocrine disruptors, 19.65–178.85 ng/L; pharmaceuticals, 17.78–67.45 ng/L; bactericides, 4.42–119.45 ng/L; personal care products, 7.79–44.10 ng/L; pesticides, 5.50–34.85 ng/L; flame retardants, 1.80–20.90 ng/L. The nitrogen pollution level surpasses that of road runoff and is predominantly attributed to WD. The detection rate of ECs is notably high, with Bisphenol A (BPA) being detected in up to 100 % of samples. Significant differences in pollutant distribution were identified between the initial and late stages of rainfall (P < 0.05). Weak first flush effects (1 < MFF20 < 2) were observed for pollutants present in the runoff of over 50 % of the rainfall events monitored. Furthermore, by controlling the initial 20 % of WD, an effective decrease in nitrogen flux below the threshold level was observed. Consequently, four modes of contaminant migration pathways and a novel strategy have been developed to guide the pollution control and sustainable utilization of roofing rainwater.