Determination of volatile organic compounds in marine biota.

A method was developed that allows the simultaneous determination of the volatile organochlorines (VOCs) chloroform, tetrachloromethane, 1, 1- dichloroethane, 1,2-dichloroethane, 1,1, 1-trichloroethane, trichloroethene and tetrachloroethene and the volatile aromatics benzene, toluene, ethylbenzene and the xylenes (BTEX) in marine biota. The biological tissue is first homogenised (at 0°C) using an ultra-turrax blender and transferred to a 25-ml EPA vial. After addition of 15 ml of water and internal standard (1,1,1-trifluorotoluene), the homogenate is treated in an ultrasonic hath (20 min at 0°C) to further disrupt the tissue. The glass vessel is then connected to a Tekmar LSC 2000 purge-and-trap apparatus coupled to a gas chromatography-mass spectrometry (GC-MS) system. The volatiles are forced out of the tissue by purging with a stream of helium gas while heating at 70°C and trapped onto a Vocarb 4000 sorbent trap. After purging, the trap is backflushed while being rapidly heated to 250°C and the analytes are desorbed and, next, trapped in a cryofocusing module (-120°C) connected to the analytical column (Restek, RTx-502.2, 60 mx0.32 mm [.D., 1.8 μm film). The analytes are injected into the column by rapidly heating the module (from - 120°C to 200°C in 0.75 min). Identification and quantification were performed with mass spectrometry operated in the electron impact mode. The method allows detection limits between 0.005 ng/g (1,2-dichoroethane, 1,1- dichloroethane and tetrachloromethane) and 0.2 ng/g (chloroform) depending on the background levels and the amount of sample. The reproducibility varies between 8.4% for toluene and 36% for chloroform and the recoveries range from 63% for trichloroethene to 115% for dichloroethane. The method was used to determine the concentrations of VOCs in Limanda limanda (dab) and Merlangius merlangus (whiting) collected at two sampling stations located on the Belgian continental shelf. Liver and muscle tissue were individually analysed in order to determine the inter-species and inter-specimen variability. The results show a considerable variability within tissues of the same species (R.S.D., 50-200%). In most cases, the concentrations of the VOCs appeared to be normally distributed. Although the levels are generally low (low ng/g range), up to 572 ng/g of tetrachloromethane was detected in the liver of whiting