Using proteolytic enzymes to assess metal bioaccessibility in marine sediments

In this work we tested two proteolytic enzymes (trypsin and pepsin) to evaluate metal bioaccessibility in marine sediments. Some working conditions were studied, in particular incubation time, enzyme concentration and solution/solid ratio, and metals release mechanisms were investigated using both untreated and denatured enzymes. The results obtained with trypsin and pepsin were compared with each other and with results from proteinase K extraction, carried out on the same sediment samples, following a procedure reported in the literature. Moreover, a comparison with the first step of BCR sequential procedure was made. Metal orders of mobility determined with the different enzymes and with acetic acid were compared with the one defined by the enrichment factors in the gut fluids of deposit-feeder organisms. The overall picture suggests that proteinase K has a better capability of reproducing natural phenomena and is therefore more suitable to determine metal bioaccessibility in marine sediments, when the target of the investigation is deposit-feeder organisms.