Heavy Metal Contamination and Potential Ecological Risks in Surface Sediments along Dar es Salaam Harbour Channel

Investigation of heavy metal contamination along Dar es Salaam harbour channel was carried out in order to determine their current concentrations, sources and potential ecological risks to benthic biota. Sampling was carried out from January to May 2019 and samples analysed using ICP-OES and C-H-N-S analyser. Analysis of heavy metal relationships showed that, Cu, Zn, Cr, As, Ni, Co, Fe, Cd had strong relationships with each other, while Pb only related to Zn. Principal component analysis partitioned metals into two groups; PC1: Ni, Cr, Fe, Co, As, Cu, Cd, and Zn explaining 73.6% variance and PC2: Pb, Zn, and Cd with 13.7% variance. Similarly, Cd, Pb and Zn had severe to very high enrichments (Cd > Pb > Zn) showing serious anthropogenic contamination of these metals in sediments along Dar es Salaam harbour channel. Degree of contamination and potential ecological risks varied from low, moderate, to high; indicating that sediments were considerably contaminated with heavy metals. Levels of contamination varied in space and according to the type of heavy metal Higher contamination and ecological risks were revealed at the harbour area probably due to the observed high concentrations of Cd, Pb and Zn. Monitoring of metals should be emphasized in order to control contaminants release into this area from their sources. Keywords: Dar es Salaam harbour channel, Heavy metals, Contamination, Sediments, Degree of contamination, Ecological risk

Diet dynamics and feeding strategies of Hilsa kelee (Cuvier, 1829) and Valamugil buchanani (Bleeker, 1853) in the Pangani Estuary, Tanzania: Insights from stomach contents and fatty acid biomarkers

Stomach contents and fatty acid (FA) biomarkers were used to investigate the diet and feeding strategies of the marine fish species Hilsa kelee and Valamugil buchanani, across three Pangani estuarine zones (about 7 km apart). The three zones depict heterogeneous distribution of trophic resources along the longitudinal estuary gradient. Despite ecological index and FA trophic niche widths indicating high overlap of trophic resources, the permutational multivariate analysis of variance revealed significant interspecific variations in diet and FA compositions. This highlights the importance of using statistically supported tools when drawing inferences on the diet dynamics of estuarine fish. The dominant diatom and detritus diets reflected the high herbivory C22:6(n-3):C20:5(n-3) and omnivory C18:1(n-9):C18:1(n-7) FA trophic indices of V. buchanani. The diatoms and copepods dominating the diet of H. kelee concurred with the species’ higher carnivory C22:6(n-3):C20:5(n-3) and lower omnivory C18:1(n-9):C18:1(n-7) FA biomarkers. The diet niche breadth index, the Amundsen feeding strategy diagrams, and the FA trophic niche suggest that V. buchanani exhibits a generalist feeding strategy, and H. kelee a mixed feeding strategy that is intermediate between a specialist and a generalist. Due to these differences, it is suggested that V. buchanani demonstrates a higher degree of resilience to anthropogenic disturbances than H. kelee in the Pangani estuary.

Histomorphological Damage in the Small Intestine of Wami Tilapia (Oreochromis urolepis) (Norman, 1922) Exposed to Microplastics Remain Long after Depuration

The histopathological effects of microplastics (MPs) in the gastrointestinal tracts of fish following long-term exposure and depuration are relatively understudied. This study investigated histomorphological damage in the small intestine of Oreochromis urolepis larvae following 65 d exposure to 38–45 μm of polyethylene microspheres (PE MPs) and after a recovery period of 60 d. Larval fish were assigned to each treatment group (control, 1, 10 and 100 PE MPs), where ingestion and degenerative changes in the small intestine were examined using a routine hematoxylin and eosin staining technique. The results highlighted significant PE MPs ingestion and retention proportional to exposure dose (χ2 = 49.54; df = 2). Villi height and width and epithelial cell height were significantly affected and differed between treatment groups. Indices of damage to the small intestine organ (χ2 = 47.37; df = 2; p < 0.05) and reaction patterns of villi, epithelial, goblet and cryptic glandular cells, leucocytic infiltration and blood congestion revealed significant occurrence of alteration as PE MPs exposure dose increased. After the recovery period, no PE MPs were observed, and villi height, width and epithelial cells showed recovery with no significant difference between treatment groups. Organ indices declined (χ2 = 12; df = 2; p < 0.05) but remained significantly different between treatment groups, largely due to leucocytic infiltration (χ2 = 9.08; df = 2; p < 0.05). The study demonstrated that microplastics induced small intestinal wall degeneration, but recovery in young fish occurred slowly. The damage likely compromised its digestive function, which may affect growth and reproduction. This requires further research.publishedVersio

Impaired Growth Performance of Wami Tilapia Juveniles (Oreochromis urolepis) (Norman, 1922) Due to Microplastic Induced Degeneration of the Small Intestine

Microplastics-induced histopathological changes in gastrointestinal tracts of fish have been widely reported. However, the translation of adverse effects in the gut to impacts on growth are understudied. This study investigated the effect of MP-induced small intestinal histomorphological changes on growth performance of Oreochromis urolepis juveniles. Sixty larvae were exposed in control (0), 1, 10, and 100 polyethylene microplastic particles (PE MPs)/mL treatment groups. On day 65, juveniles were euthanized, dissected, and biometric data were taken. Small intestine histomorphological lesion index (HLI) was calculated following histological preparation using routine hematoxylin and eosin procedure. Results showed increase in HLI proportional to PE MPs exposure dose. These deteriorations equally reduced growth in final weight, weight gain and total length (One-Way ANOVA, p > 0.05), and Specific Growth Rate (SGR) (Kruskal–Wallis Test, p > 0.05), though there were insignificant differences between treatment groups. Condition factors of fishes in control and 1 PE MPs differed significantly and with other treatment groups (Tukey HSD, p < 0.05). Small intestines HLI correlated significantly with growth pattern (Spearman, r = 1.00, p = 0.01), condition factors (Pearson, r = −0.995, p < 0.05), final weight, weight gain, and total length (Spearman, r = −1.00, p = 0.01) but not with SGR. The allometric growth pattern changed towards isometric corresponding to increasing HLI. These findings suggest that MPs damaged small intestine structure and thus impaired digestion and nutrients absorption functions which disrupted growth. Such effects may impair juveniles’ ability to escape enemies, find food, and eventually reproduce, and therefore require further study.publishedVersio

Temporal and spatial distribution of trace metals in the Rufiji delta mangrove, Tanzania

Spatial and temporal distribution of trace metals and their cycling is a key issue for understanding the ongoing biogeochemical processes in coastal environments. Sediment cores were collected from six different sampling locations from the Rufiji delta mangrove forests in southeastern coastal Tanzania that are perceived to be impacted by urban development and agricultural activities in the catchment, and pollution in upstream sections of the Rufiji River. The chronology and sediment accumulation rates at these sampling sites were derived based on the distribution of Pb-210(excess) method. The trace metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were sequentially extracted as per the BCR method and analyzed. The results indicate that the mass accumulation rates range from 0.40 g cm(-2) year(-1) (cores NR3 and NR4) to 1.75 g cm(-2) year(-1) (core SR1). Trace metals in the cores are mainly associated with the residual phase and their abundances in sediments are ranked as Cr amp;gt; Zn amp;gt; Ni amp;gt; Cu amp;gt; Pb amp;gt; Cd. The results imply that trace metals in the Rufiji delta mangroves are mainly of crustal origin, and they are less sensitive to weathering. Further, these metals are least available for uptake by plants and they pose limited threat to the biota.Funding Agencies|Swedish Research Link project-Africa [348-211-7408]; Western Indian Ocean Marine Science Association (WIOMSA); MARG 2</p