Heavy Metals, Polycyclic Aromatic Hydrocarbons and Organochlorine Compounds in Queen Scallop (Aequipecten Opercularis) for Human Consumption.

Abstract

Results of chemical concentrations of heavy metals, polyciclyc aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloretane (DDT) and its metabolites in queen scallop (Aequipecten opercularis) are presented. Sampling took place, after the spawning period, in the main shellfish grounds of the Rias of Vigo and Arosa (NW Spain). Each sample was prepared from 20 individuals representing the available size range existing in the selected area. The soft tissues (total edible portion) were separated from the shells, triturated with an Ultraturrax homogeniser and freeze-dried. The analysis of trace metals includes a nitric acid digestion in a microwave. The quantification was carried out by atomic absorption spectrometry with Zeeman effect graphite furnace. Total mercury was determined by flow injection cold vapour atomic absorption spectrometry. The method used for the determination of 13 Polycyclic Aromatic Hydrocarbons (PAHs) is based in a Soxhlet extraction with organic solvents mixture, followed by an extract cleaning up using column chromatography. Finally, the extract was analysed using gigh performance liquid chromatography with wavelength programmable fluorescence detector. Samples for analyses of PCBs were extracted in a Soxhlet apparatus with organic solvents mixture. Clean-up and fractioned of the extract was performed with a chromatographic columns. The extract were analysed by gas chromatography with an electron capture detector using capillary columns and He as carrier gas. The lipid content was gravimetrically determined. The quality of the chemical analyses is demonstrated by the results obtained in different intercalibration exercises that take part on a regular basis, such as QUASIMEME. The internal laboratory QC includes analyses of duplicate samples and procedural blanks as well as control charts of CRMs. The experimental values for metals were far below the EU maximum levles for bivalve molluscs for human consumption, with the exception of Pb, for which some results exceeded EC Regulation Nº 1881/2006. The Pb values appear to be more related to the biology of this species than to the contaminant levels in the study areas, as the Pb values in other species of bivalve molluscs from these areas show concentrations far below the limits for consumption. The average As and Zn concentrations was higher in Arosa than in Vigo. Cd, Hg and Cu showed very similar values in both areas of study. For PAHs, the comparison value used in this study was the one established for extraction and consumption after the Erika and Prestige oil spills, 200µg kg-1 dry wt in Vigo, which is 3-4 times less than the limit, to 151-181 µg Kg-1 dry wt in Arosa, which is very close to, but below the maximum allowed level. In general, the queen scallop showed higher PAH concentrations in Arosa than in Vigo, and the origin also appears to be different. The highest concentrations of PCBs were found in the Ría of Vigo, zone with greatest industrial and port activity, with a maximum value of 20 µg Kg-1 wet wt, which is considerably lower than the level established by the FDA for edible seafood. In the Ria of Arousa the concentrations were 6-7 times lower, with values ranging level 2.8 and 3.2 µg kg-1 wet wt. The concentrations of DDTs showed similar values in the two rias: 0.52-0.64 µg kg-1 wet wt in the Ria of Vigo and 0.45-0.55 µg kg-1 wet in the Ria of Arosa. The levels were also lower then the maximum limits established by the EU.