Fertilizers as a Source of Melamine and Cyanuric Acid in Soils: A Nationwide Survey in China

The use of melamine and cyanuric acid in agriculture, industry, and consumer products has led to their ubiquitous environmental distribution. Nevertheless, little is known about the contamination of soils by melamine and cyanuric acid. Contamination of soils with melamine can lead to plant uptake and food chain transfer of these chemicals. In this study, concentrations of melamine and its three derivatives (cyanuric acid, ammeline, and ammelide) were determined in 98 surface soils and 16 fertilizers collected across China in 2017. Elevated concentrations of Sigma melamine (sum of melamine and its three derivatives) were found in soils at concentrations that ranged from 8.67 to 2020 ng/g dry weight (dw), with an average value of 213 ng/g dw. Melamine accounted for 63% of the total concentrations in soils, which was followed by cyanuric acid (28%). Elevated concentrations of melamine and cyanuric acid were found in nitrogenous fertilizers such as nitrolime (n = 3; mean: 284 mu g/g) and urea (n = 4; mean: 3160 mu g/g), respectively. The measured concentrations in fertilizers were 3 to 4 orders of magnitude higher than those found in soils. Farmland soils (mean: 545 ng/g dw) contained significantly higher concentrations of Sigma melamine than those of urban and background (forest) soils (92.5 ng/g dw). Our findings suggest that fertilizers are an important source of melamine and cyanuric acid in farm soils. Spatial distribution of melamine and cyanuric acid in soils showed the highest concentrations in eastern China, which corresponded well with population density, industrial, and agricultural activities. An ecological hazard assessment was performed of melamine in soils through a hazard quotient (HQ) approach. The mean HQ value was 0.35, and 7 of 98 surface soils had values above 1. Further studies are needed to discern uptake of melamine and its derivatives by crops and the fate of these chemicals in agricultural ecosystems.