Using Posidonia oceanica (Linnaeus) Delile as a biomonitor of heavy metal pollution in Maltese coastal waters

Abstract

Seagrasses, including Posidonia oceanica, act as heavy metal bioaccumulators. The present study, therefore, assessed the use of P. oceanica as a biomonitor of heavy metal pollution in Maltese coastal waters. P. oceanica and sediment samples were collected from Cirkewwa, Wied iz-Zurrieq, Qalet Marku, Anchor Bay and Marsaxlokk in October 2008, February 2009 and June 2009. Various P. oceanica descriptors were determined. These include leaf type and surface area; percentage necrosis; percentage epiphytes and coefficient A (percentage of leaves that have lost their apex). The P. oceanica shoots were fractionated into: adult leaf apical end, mid-section and basal end; rhizome; epiphytes; and remaining leaves (intermediate and juveniles). The P. oceanica fractions and sediment samples were digested and analysed for cadmium, copper, lead and zinc using voltammetry. The digestion procedure for P. oceanica samples was purposely devised for this study. The results indicate that Cirkewwa and Wied iz-Zurrieq are the least impacted sites. P. oceanica from Marsaxlokk show the lowest vitality, as evidenced through the Ecological Quality Ratios (EQR), and the highest metal contamination reflected in the Metal Pollution Indices (MPT). When comparing data from Qalet Marku and Anchor Bay, samples from Qalet Marku have the highest MPI, whilst P. oceanica from Anchor Bay show the lowest EQR values. This could be a result of either the presence of other contaminants to the metals analysed at Anchor Bay, or the increased effect of cadmium upon growth at Anchor Bay where elevated concentrations are found. The present study showed that levels of lead in P. oceanica are comparable to levels in other Mediterranean regions that are considered as hotspots for this pollutant. Levels of zinc have been found to be relatively low and generally similar to Mediterranean regions considered Lo be non-contaminated. Local levels of cadmium and copper varied with location.