Virus,protozoa and organic compounds decay in depurated oysters

Aims

(1) Evaluate the dynamic of the depuration process of Crassostrea gigas oysters using different ultraviolet doses with different amounts of contaminants (virus, protozoa and organic contaminants) and (2) investigate the morphological changes in the oysters' tissues produced by the depuration procedures.

Methods

The oysters were allocated in sites with different degrees of contamination and analyzed after 14 days. Some animals were used as positive controls by artificial bioaccumulation with HAdV2 and MNV1 and subjected to depuration assays using UV lamps (18 or 36 W) for 168 h. The following pollutants were researched in the naturally contaminated oysters, oysters after 14 days in sites and oysters during the depuration processes: virus (HAdV, HAV, HuNoV GI/GII and JCPyV), by (RT) qPCR; protozoa (Cryptosporidium and Giardia species), by immunomagnetic separation and immunofluorescence; and organic compounds (AHs, PAHs, LABs, PCBs and organochlorine pesticides—OCs), by chromatography. Changes in the oysters' tissues produced by the depuration processes were also evaluated using histochemical analysis by light microscopy. In the artificially bioaccumulated oysters, only HAdV2 and MNV1 were investigated by (RT) qPCR before the depuration procedures and after 96 and 168 h of these procedures.

Results

At 14 days post-allocation, HAdV was found in all the sites (6.2 × 105 to 4.4 × 107 GC g^− 1), and Giardia species in only one site. Levels of PCBs and OCs in the oyster's tissues were below the detection limit for all samples. AHs (3.5 to 4.4 μg g^− 1), PAHs (11 to 191 ng g^− 1) and LABs (57 to 751 ng g^− 1) were detected in the samples from 3 sites. During the depuration assays, we found HAdV, Giardia and Cryptosporidium species until 168 h, independent of UV treatment. AHs, PAHs and LABs were found also after 168 h of depuration (36 W and without UV lamp). The depuration procedures did not produce changes in the oysters' tissues. In the artificially contaminated and depurated oysters, we detected HAdV until 168 h and MNV1 until 96 h of depuration.

Conclusion

The applied depuration treatments were unable to eliminate the protozoa or to degrade the HAdV genomes but were able to degrade the MNV1 genomes. Similarly, the UV water treatment was not efficient for aliphatic hydrocarbons, PAHs and LABs, as their concentrations were equivalent or higher to the concentrations of the control samples and samples from depuration tanks without UV treatment.