Calibration of metals against salinity and high turnover of nickel in marine bivalves

Abstract

Despite salinity has been well documented for its significant effects on the bioaccumulation of trace elements in marine bivalves, we identified a species whose metal burden was less influenced by salinity – black mussel Septifer virgatus. According to the biokinetics modeling, the weak salinity effects on the tissue concentration of Ni and Zn can be explained by the synchronized variations of waterborne uptake and elimination under the influence of salinity, since both their rates of uptake and efflux were negatively correlated with salinity. In contrast, salinity can significantly influence the metal accumulation of oyster Crassostrea hongkongensis, suggesting potential interference for biomonitoring. For the first time, we established a novel method to calibrate biomonitoring data against salinity. Relationships between tissue metal concentration and biological proxy for salinity (tissue Na) are required in field calibration, which were quantified based on laboratory exposure experiment. The method was applied to the biomonitoring of Pearl River Estuary, and verified to be feasible and effectively reduces the influence of salinity. The behavior of Ni in oyster C. hongkongensis is different from other metals that have been studied. A 4-week waterborne exposure at 3 different concentrations demonstrated that Ni in oysters reached steady-state rapidly. The efflux rate constant (k_e) determined through a 30-day depuration was positively correlated with tissue concentration, with the highest k_e reaching 0.155 d^-1. Pre-exposure to Ni significantly reduced the dissolved uptake, probably accompanied with depressed filtration activity. Ni in oysters was predominantly in detoxified fractions, among which metallothionein-like protein (MTLP) was the most important one for binding. The high proportion of Ni in MTLP was further presumed to contribute to the rapid elimination. Overall, Ni in oysters can be regulated by enhanced efflux, suppressed uptake, and sequestration of most Ni into detoxified pool.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology