Occurrence of matrix-bound phosphine in intertidal sediments of the Yangtze Estuary

This study investigated the levels and potential transformation of matrix-bound phosphine in the intertidal sediments (0-5 cm) of the Yangtze Estuary. Matrix-bound phosphine concentrations in sediments ranged from 0.65 to 3.25 ng kg^-1, with an annual average of 1.53 ng kg^-1. In freshwater sediments, the concentrations of matrix-bound phosphine were significantly higher than in the brackish sediments. The maximum concentrations of matrix-bound phosphine appeared in July (1.17-3.25 ng kg^-1), followed by May (0.92-3.01 ng kg^-1), November (0.65-2.41 ng kg^-1) and January (0.51-1.42 ng kg^-1). Matrix-bound phosphine derived probably from the mechanochemical reduction of apatite-bound phosphate and the microbial conversion of organic phosphorus in the intertidal sediments. Its spatial and seasonal distributions, however, were regulated by salinity and sediment temperature. Compared with other aquatic systems (e.g. rivers, lakes and coastal seas), a low level of matrix-bound phosphine was observed in the intertidal sediments, probably implicating a relatively rapid turnover of phosphine in the system.