Abstract
In the Anthropocene era, an immersion of toxic substances, i.e., trace metals, has been enhanced in the marine environment not only due to urban sprawl and industrial development but predominantly owing to incongruous management and lack of sustainable approaches. The coastal region of Pakistan shares a similar obstacle as most of the developing countries confronted. Therefore, this study was designed to investigate concentrations of eight metals (Cu, Fe, Zn, Ni, Co, Pb, Cr, and Cd) in sediment and Dotillid crab, Ilyoplax frater, at three tidal creeks in Karachi, Pakistan. All metals in sediments and crabs were analyzed by atomic absorption spectrometer. The sediment pollution was evaluated by contamination degree (CD) and potential ecological risk index (RI). After depicting the metal pollution in sediments, metal accumulation, and contamination in benthic crab were investigated through total metal concentrations in crabs, accumulation factor (AF), correlation analysis, and regression analysis. The results exhibited substantial differences in the concentrations of Zn, Ni, Pb, Cr, and Cd among the tidal creek sediments. Contamination factors indicated that the Cd and Pb had the highest sharing in sediment pollution, and the tidal creeks classified as moderately contaminated. All metal accumulations in Dotillid crabs showed notable spatial variations, and accumulation factors (AFs) for most of the metals were > 1.0, signifying the strong bioaccumulation of metals in crabs. Particularly, Cu, Co, and Cd levels were considerably greater (two to three times) in Dotillid crabs compared to creek’s sediments, even though they don’t share any relationship between two matrixes. Hydrographical and sedimentological traits also revealed significant interactions with metal levels in sediments and crabs. A substantial association was also noticed in Fe, Ni, and Pb between sediments and crabs. Interestingly, most of the metal AFs showed a notable inverse correlation with the environmental matrix. Exceptionally, a strong positive correlation found between the Pb concentration in crabs and sediments suggested that I. frater probably acts as an indicator of Pb pollution.
Highlights
Trace metals are among the most hazardous contaminants in the environment because of their perseverance, biogeochemical cycling, and the ecological risks they pose [12, 64, 81]
The aims of the current study were (1) to scrutinize contamination by eight metals (Cu, Cd, Cr, Co, Ni, Zn, Pb, and Fe) in sediments from three contaminated tidal creeks, Karachi, Pakistan, (2) to analyze the bioaccumulation of these metals in the resident deposit feeder crab species I. frater related to the sediment concentrations, (3) to evaluate the impacts of environmental heterogeneities on metal the distribution in sediments as well as crab, and (4) to identify the potential of this crab species as a biomonitor for heavy metal contaminated environments, by evaluating the relationship between metal concentrations in crabs and exposure concentrations in the sediment
A slightly acidic environment found at S2 as compared to the other two sites may have resulted from the decaying of the domestic and industrial waste litter in the study site contributing to the acidic nature of the groundwater
Summary
Trace metals are among the most hazardous contaminants in the environment because of their perseverance, biogeochemical cycling, and the ecological risks they pose [12, 64, 81]. Sediments are a significant carrier for trace metals in marine environments, and heavy metals may be transported into these environments associated with deposits. After resuspension of sediments, dissolved and particulate fractions of metals are released into the water. Given the potential adverse effects of trace metals in a range of aquatic organisms, there is a critical need for biomonitoring of these contaminants, as a prerequisite to initiating management actions
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