Lead (Pb) contamination trends in Msimbazi estuary reconstructed from 210Pb-dated sediment cores (Msimbazi River, Tanzania)

Abstract

Urbanization and the concentration of industrial sites in coastal regions have led to a strong risk of heavy metals contamination in the neighbouring marine environment. Analysis of dated sediment cores from these environments may allow historical trends of heavy metal input to be reconstructed, and recent and historical inputs of metal contaminants to be compared. In this work we have assessed the depth profile of lead concentrations; converted lead profile to time-based profiles using 210Pb sediment dating method; established site-specific baseline value for lead and estimated lead enrichment factors (EF) in sediment cores from Msimbazi estuary in Tanzania. The core bottom was estimated to date back about 59 years. Lead concentrations ranged from 11.5 (mgkg−1 DW) in 1961 to 50.1 (mgkg−1 DW) in 2006. Sediment layers deposited during late 1950`s and 1960`s were assumed to represent baseline values of lead concentrations because they correlate well with the documented population growth and increase of industrial and agricultural activities in the catchment. Iron-based enrichment factors illustrate that no enrichment of lead (EF ≤ 1) between 1957 and 1971. The upper sections of the core indicate that sediments of Msimbazi have experienced minor (1 < EF < 3) to moderate (3 ≤ EF < 5) enrichment of lead over time.