Comparative analysis of trace metal levels in the crab Dotilla fenestrata, sediments and water in Durban Bay harbour, Richards Bay harbour and Mlalazi estuary, Kwazulu-Natal, South Africa

Abstract

Durban Bay and Richards Bay Harbours are the largest and most economically active shipping harbours in South Africa supporting a diversity of ecosystems and biota of ecological importance. This study assessed and compared levels of metals in selected tissues of the sand bubbler crab ( Dotilla fenestrata ), water and sediments from anthropogenically impacted Durban and Richards Bay Harbours with those of Mlalazi estuary, a considered pristine site due to its sheltered catchments. Metal concentrations (Cd, Cu, Pb and Zn) were investigated using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). Metals concentrations in crab tissues were as follows; exoskeleton > gill > digestive gland, metal concentrations in tissues followed the order Cu > Zn > Pb > Cd. Metal levels in crabs from Durban Harbour (Cd 0.42, Cu 83.8, Pb 2.43and Zn 6.4 μg/g) were significantly higher than Richards Bay (Cd 0.22, Cu 27.7, Pb 1.23 and Zn 9.54 μg/g) and Mlalazi estuary (Cd 0.17, Cu 18.7, Pb 3.53 and Zn 6.91 μg/g). Metal levels in sediments followed the order Zn > Cu > Pb > Cd. Mlalazi had significantly elevated metal levels in sediment (Cd 6.83, Cu 35.63, Pb 33.43 and Zn 56.27 μg/g) compared to Durban Harbour (Cd 2.73, Cu 16.07, Pb 12.20 and Zn 38.70 μg/g) and Richards Bay (Cd 3.10, Cu 16.00, Pb 11.43 and Zn 26.07 μg/g). Metal concentrations in water were Cu > Zn > Pb > Cd save Mlalazi estuary with significantly higher Zn levels. Mlalazi estuary, the considered pristine site had significantly elevated metal levels in the sediments and water compared with the impacted sites; however, had significantly lower metal levels in the crabs’ tissues due to lower metal bioavailability. Factors such as high natural metal concentrations, metal speciation, sediment grain and organic matter content could possibly account for high metal concentrations without corresponding bioaccumulation and magnification in crabs from Mlalazi estuary.

On the Road to Sustainable Water Supply: Reducing Public Health Risks and Preserving Surface Water Resources in the Milluni Micro-Basin, Bolivia

“…At the same time, the parameters measured in situ were statistically analyzed to assess whether they can be indicators of the presence of heavy metals, to optimize resources during future monitoring. The development described below is based on a statistical analysis of similar problems from other studies in other parts of the world [41][42][43].…”

Portunus pelagicus (Linnaeus, 1758) as a Sentinel Species to Assess Trace Metal Occurrence: A Case Study of Kuwait Waters (Northwestern Arabian Gulf)

“…The inverse relationship between the high heavy metal concentrations in sediments and noticeably low metal concentrations in the crab organs from the Al-Khiran Area compared to those from the Shuwaikh and Shuaiba Ports areas could point out the geological aspects. Consequently, they arise naturally in naturally high background levels of metals in the Al-Khiran Coastal Area, which could firmly influence the bioavailability of heavy metals, as the free ionic forms are consistently the most bioavailable [ 113 , 114 ]. Consequently, there is generally a strong negative relationship between the grain size of sediments and heavy metal concentrations [ 115 , 116 ].…”