Comparison of oil exposure methods to filter feeding bivalve

Abstract

Oyster, a representative filter feeder is commonly used for environmental monitoring. After the Hebei Spirit Oil Spill (HSOS), long term monitoring of petrogenic PAHs using oyster showed persistently high concentration for more than one year which could not be explained by the traditional oil exposure scenario. This study aimed to compare various exposure methods including water accommodated fraction (WAF), mechanically dispersed oil (MDO), and oil-SPM aggregates (OSA), and to measure petroleum hydrocarbons accumulated in oyster according to exposure method. Oil concentrations used were 24 g/l for WAF and MDO, 0.12 g/l for OSA respectively. Oysters were exposed to WAF, MDO and OSA for 48 hours and this test was performed in triplicate. Concentration of petroleum hydrocarbons (TPH, UCM, 16 PAHs, alkyl PAHs) in oysters exposed were in the order of MDO>OSA>WAF. Accumulated concentrations of TPH and PAHs in oysters exposed to OSA were as high as half of those exposed to MDO although only 1/200 of oil was used for OSA. This result implied that OSA is the more vulnerable form of exposure to filter feeding oyster. Composition profiles of petroleum hydrocarbons in oyster exposed to MDO and OSA were similar with exposed oil. This similarity was also found at field collected oysters right after the spill. Meanwhile, oysters exposed to WAF only showed low molecular weight hydrocarbons with relatively high solubility. Oil fingerprinting ratio plots revealed that oysters exposed to MDO and OSA has similar composition profiles that of oil. These results suggest that right after the HSOS, intertidal oysters were exposed to dispersed MDO or OSA. OSA could be preferentially formed in the turbid environment, and our study revealed that OSA may act as a continuous route of exposure to filter feeders.