The total metal concentrations (Cd, Cu, Pb, Zn, Mn, Ni, Cr, and Fe) in the mesozooplankton (200 μm–2 mm) were studied for a year in a human-impacted estuary strongly affected by urban and industrial discharges located in the South Atlantic. Over the last 25 years, this estuary has been the site of significant anthropogenic impacts including industrial activities, maritime traffic, and regular dredging. A quantitative and qualitative analysis was also carried out to identify the mesozooplanktonic community that was sampled for metal determinations. The mesozooplankton had high concentrations of toxic metals such as Cd, Pb, Cr, and Ni, which may indicate that these organisms are strong accumulators of these metals. Also, the analyzed metals had a wide temporal variation, the highest levels being in autumn and spring. The ranges were as follows: cadmium (Cd): 0.3–3.8; copper (Cu): 35.3–226.6; chromium (Cr): 1.4–57.9; iron (Fe): 1060–57370; manganese (Mn): 18–1102; nickel (Ni): 2.8–57.3; lead (Pb): 2.4–66.7; zinc (Zn): 97.6–1872.2 (μg g –1dry weight). Total zooplankton abundance also showed a significant temporal variation and the most important taxa were the copepods Acartia tonsa, Eurytemora americana, the barnacle Balanus spp. (in the nauplius larval stage), and the crab Cyrtograpsus altimanus (in the zoea larval stage).
In zooplankton, all the metals were detected throughout the whole sampling year and at all sampling sites, which suggests the presence of continuous or quasi-continuous sources of these contaminants. Thus, the most abundant zooplankton species could be considered as potential biomonitors for trace metals in heavily impacted marine environments like estuaries.