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Spatial distribution of lead in surface and deep sediments of the semi-enclosed bay influenced by the anthropogenic activity (Kastela Bay, Croatia)

The area around the Kastela Bay is heavily exposed to anthropogenic activities representing the sources of contaminants to the bay. We studied the spatial distribution of lead in the sediments at three depths (0–5 cm, 5–10 cm, 40–50 cm), to determine i) whether lead disperses in the bay or it accumulates on the localized sites and ii) to establish the sediment condition regarding pollution. Samples were collected on 95 sampling stations disposed in a regular grid covering the bay. Lead concentrations were measured by the energy dispersive X-ray fluorescence technique. Enrichment factors were calculated to differentiate natural and anthropogenic origin of lead. The reference element was aluminium and the reference material was the unpolluted, preindustrial sediment from the Kastela Bay. The degree of sediment pollution was also assessed using geoaccumulation indices and comparing lead concentrations with recommended values of the sediment quality guidelines. Maps of lead concentrations, enrichment factors, and geoaccumulation indices were presented. Lead concentrations were in the range <1.6–142 mg/kg. Maximum content was higher than the upper limit of guidelines recommended values (30.2 mg/kg or 50 mg/kg). Mean values of enrichment factors were in the range 3.5–6.9 and the maxima in the range 23–68, suggesting the presence of lead from anthropogenic sources. Mean values of the geoaccumulation indices were in the range -0.065–1.6 and maxima in the range 3.9–5.4. This points to very polluted to extremely polluted sediment levels. The east part of the bay is the most polluted one. The area of polluted sediments increases with decreasing sediment depth. Lead distribution was found to depend on sediment grain size, sampling depth, and location of point pollution sources. Lead is generally dispersed in the Kastela Bay but accumulates only on a few sites.

Croatia; Enrichment factor; Geoaccumulation index; Kastela Bay; Lead

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