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Occurrence and risk assessment of p-phenylenediamines and their quinones in aquatic environment: From city wastewater to deep sea
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Researchers measured levels of p-phenylenediamines and their chemical byproducts, which are emerging pollutants derived from rubber and tire wear, across wastewater treatment plants and deep-sea sediments. They found these compounds present throughout the water pathway from urban sewage to the ocean floor, with some posing moderate to high ecological risk. The study highlights tire-derived chemicals as a widespread and underappreciated source of aquatic contamination.
p-Phenylenediamines (PPDs) and PPD-derived quinones (PPD-Qs) have been considered emerging pollutants recently. Their available data on sediment and sewage sludge are limited, especially the ecological risks. Here, typical PPDs and PPD-Qs were measured in the sludge of wastewater treatment plants and surface sediment of a developed river basin (including reservoirs, estuaries, and rivers) and deep-sea troughs. The total concentrations of PPDs (∑PPD) were highest in sludge (range: 9.06-248 ng g), followed by surface sediment of the Dongjiang River basin, China (3.33-85.3 ng g), and lowest in sediment of the Okinawa Trough (0.01-7.46 ng g). The median value of ∑PPD in surface sediment of rivers (9.54 ng g) was higher than those in reservoirs (4.28 ng g) and estuaries (5.26 ng g). N-(1,3-Dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) was the major congener in all samples, accounting for over 60 % of ∑PPD. For quinones, 6PPD-Q and IPPD-Q were frequently detected in sludge, only trace 6PPD-Q was detected in the sediment of estuaries (nd-0.62 ng g) and rivers (nd-5.24 ng g), and both of them were absent from the sediment of the Okinawa Trough. The occurrence of PPDs in the trough may be the in-situ release of microplastics, and due to the low-light and weak alkaline conditions of deep-sea water, quinones may hardly photodegrade from PPDs. The PPD concentrations in sludge were positively correlated with local GDP, and the annual PPD emission from sludge will exceed 1370 kg in China. The results of ecological risk assessments indicated low risks for PPDs in sludge-amended soil, median risks for several PPDs in river sediment, but median to high risks for 6PPD-Q contamination sludge-amended soil. For the first time, we explored the potential environmental risk of PPDs and related quinones in sludge used as a soil conditioner.
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