Measuring Pollutants in Urban River Sediments

Title: Organophosphate Diesters in Urban River Sediment from South
China: Call for More Research on Their Occurrence and Fate in Field

Authors: Chan Liang, Bo Peng, Gao-Ling Wei, Yanyan Gong, Guoqiang Liu, Lixi Zeng, Liang-Ying Liu, and Eddy Y. Zeng

Journal: ACS EST Water 2021, 1, 4, 871–880

Organophosphate triesters are used as flame retardants, as well as industrial applications, and have become prominent in hopes of replacing older, environmentally persistent polybrominated diphenyl ethers. However, despite a 7X increase in their production in the last decade, organophosphate triesters have been implicated as being potentially dangerous to human health. Additionally, they can break down into organophosphate diesters, which may have more severe toxic effects.

 Figure 1: Generic organophosphate triester (left) and organophosphate diester (right)

            Because organophosphate diesters have previously been found in high levels in household dust and sewage, researchers decided to measure the concentration of these pollutants in river sediment in an urban river exposed to high levels of potential pollutants. They collected samples from six districts in Guangzhou, China. After extracting the organophosphate di and triesters from the samples, they subjected each sample to liquid chromatography, which separates out individual molecules and produces a signal proportional to their concentration three times. The spectra produced were used to determine the concentration of the di and triesters by comparison to spectra produced using known concentrations of commercial standards. 

            Analysis of the data showed that large variation between the high and low measurements for triesters both in the urban river sediment tested in this study as well as in previously reported concentrations around the world. Comparing the different locations showed that the urban river sediment tested showed similar concentrations of organophosphate triesters as many other rivers near population centers around the world, although higher concentrations than open ocean of large lakes (Figure 1). Although other studies have found that there was some correlation between the total organic content of a waterbody and the amount of organophosphate triesters, that was not true for the urban rivers sampled here.

Figure 2: Concentration of organophosphate triesters at different locations. Note that due to large variation, the y-axis is in log scale.

            The authors also looked at the concentration of organophosphate diesters in the sediment compared to other common sources of exposure including dust, found in homes, cars, and workplaces, and sludge, such as that found in sewage and wastewater. They found the concentration in the river sediment was lower than in dust from a variety of locations including homes, cars, and offices but higher than that in sludge, indicating that the pollutant may be persisting in the environment once it makes its way to rivers. In general, samples that showed a high liver of organophosphate triesters also showed increased levels of many of the organophosphate diesters tested, indicating that the triester may be decomposing to the diester under the environmental conditions present in the river sediment.

            The authors note that more study is needed into the origin of the phosphonate diesters found in sediment, which could come from degradation of the triesters but could also be produced by impurities in commercial products containing organophosphate triesters or from commercial use of the diesters themselves, for example in paints and coatings. Another pressing concern is the development of safe methods, whether physical, chemical, or microbial to degrade the organophosphate triesters into benign materials rather than permitting release into the environment where they may accumulate and degrade into the more toxic organophosphate diesters.

Image Credit: Sergei Gussev, wikicommons

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