On the other hand, when comparing sites in order to assess the
contamination input by creeks outfalls, the highest PCB levels can
be observed in B. rodriguezii collected at LC and S (Table 2). First,
this result indicates that PCB distribution in the studied area is not
regulated by the degree of urbanization, as LC flows through urbanized
area and S does not. Instead, higher PCB levels and
congener distribution pattern indicate the presence of point sources
at LC and S. In most cases tri and hexa-chlorinated homologues
predominated in mollusc samples (S. lessoni: 27e35% and 31e37%,
respectively; B. rodriguezii: 32e44% and 30e39%, respectively)
(Fig. 4).