Distribution of arsenic, silver, cadmium, lead and other trace elements in water, sediment and macrophytes in the Kenyan part of Lake Victoria: spatial, temporal and bioindicative aspects

Modelling Euphrates river water quality index based on field measured data in Al-Diwaniyah City, Iraq

Pollution monitoring in surface water using field observational procedure is a challenging matter as it is time consuming, and needs a lot of efforts. This study addresses the challenge of efficiently monitoring and predicting water pollution using a GIS-based artificial neural network (ANN) to detect heavy metal (HM) pollution in surface water and effect of wastewater required discharge on the Euphrates River in Al-Diwaniyah City, Iraq. The study established using 40 water sampling stations and incorporates Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-OES) to assess HM levels. An ANN model suggested to estimate Heavy Metal Pollution Index (HPI) considering physiological and chemical factors. It formulates six scenarios to enhance HPI prediction accuracy, utilizing ANN in MATLAB for modeling and GIS statistical tools with inverse distance weighted (IDW) methods for a comprehensive assessment. The developed approach predicted HP concentration in the Euphrates River basin in an actual case study. The validation of the predictive maps between the theoretical and practical part is performed by monitoring 16 stations and conducting laboratory analyses, resulting in acceptable coefficients of determination (R2), observations standard deviation ratio (RSR), and Nash-Sutcliffe efficiency coefficients of 0.999, 1, and 0.99, respectively indicates that reliable forecast results closely match observed data from monitoring stations. The study identifies that nickel, iron, and cadmium concentrations exceeded Iraqi and World Health Organization (WHO) standards, leading to a heavy pollution index peak of 150.38 in the Euphrates River branch. In this study, the HPI is used to identify areas with high pollution levels, validate the accuracy of the ANN model for prediction, and generate a pollution map to visualize pollution levels.

Exploring the Microbial Ecology of Water in Sub-Saharan Africa and the Potential of Bacteriophages in Water Quality Monitoring and Treatment to Improve Its Safety

Access to safe water and food is a critical issue in sub-Saharan Africa, where microbial contamination poses significant health risks. Conventional water treatment and food preservation methods have limitations in addressing water safety, particularly for antibiotic-resistant bacteria and other pathogenic microorganisms. This review explores the potential application of bacteriophages as an innovative solution for water treatment and food safety in the region. Bacteriophages specifically infect bacteria and offer a targeted approach to reducing bacterial load, including multidrug-resistant strains, without the drawbacks of chemical disinfectants. This review also highlights the advantages of phage bioremediation, including its specificity, adaptability, and minimal environmental impact. It also discusses various case studies demonstrating its efficacy in different water systems. Additionally, we underscore the need for further research and the development of region-specific phage applications to improve water quality and public health outcomes in sub-Saharan Africa. By integrating bacteriophage strategies into water treatment and food production, the region can address critical microbial threats, mitigate the spread of antimicrobial resistance, and advance global efforts toward ensuring safe water for all.

Seasonal assessment of surface water and sediments pollution in Rachiine River, Northern Lebanon, using multivariate statistical analysis

Urbanization has caused severe negative impacts on intra-urban river water worldwide. In this study, the WHO drinking water standards (2024) were used as reference to assess the physicochemical properties, heavy metals (HMs) content and microbial load in water and sediment samples collected from 25 locations along Rachiine River, located in Northern Lebanon, during wet and dry periods. Multivariate statistical analysis was applied to evaluate the seasonal variations in water and sediment quality, and determine the pollution sources. The microbial load assessment indicated high pollution levels by Escherichia coli, fecal enterococci, total coliform and fecal coliform, which generally increased as the river progressed downstream. Cluster analysis (CA) provided three major clusters in the study region, representing the northern, central, and southern sectors of the river. Principal components analysis (PCA) of water samples generated four principal components (PCs) accounting for 64.3, 11.4, 7.6 and 4.1 % of the total variance, whereas PCA of sediment samples explained 59.1, 16.9 and 11.1 % of the data set variance. These PCs revealed that the quality of water and sediments is significantly impacted by point and diffuse sources, including geological and anthropogenic factors. These findings call for urgent management strategies to limit future deterioration of the aquatic bodies.

Increasing mercury bioaccumulation and biomagnification rates of Nile perch (Lates niloticus L.) in Winam Gulf, Lake Victoria, Kenya

The Nile perch (Lates niloticus L.) commercial fishery for Lake Victoria in East Africa is an important source of revenue and employment. We focused on shifts in food web structure and total mercury (THg) bioaccumulation and biomagnification in Nile perch, and lower food web items collected from Winam Gulf (Kenya) sampled 24 years apart (1998 and 2022). Stable isotope carbon (δ13C) values were higher in all species from 2022 compared to 1998. Stable nitrogen isotope (δ15N) values in baseline organisms were lower in 2022 compared to 1998. In Nile perch, δ15N values were correlated with total length, but the δ15N-length regressions were steeper in 1998 compared to 2022 except for one large (158 cm) Nile perch from 1998 with an uncharacteristically low δ15N value. Total Hg concentrations were lower in lower trophic species from 2022 compared to 1998. However, the THg bioaccumulation rate (as a function of fish length) in Nile perch was greater in 2022 compared to 1998 resulting in 24.2 % to 42.4 % higher wet weight dorsal THg concentrations in 2022 Nile perch for market slot size (50 to 85 cm) fish. The contrasting observations of increased THg bioaccumulation with size in 2022 against decreases in the rate of trophic increase with size and lower THg concentrations of lower food web items imply reduced fish growth and potential bioenergetic stressors on Winam Gulf Nile perch. All samples except 1 large Nile perch (139 cm total length collected in 2022) had THg concentrations below the European Union trade limit (500 ng/g wet weight). However, for more vulnerable individuals (women, children and frequent fish eaters), we recommend a decrease in maximum monthly meal consumption for 55-75 cm Nile perch from 16 meals per month calculated for 1998 to a limit of 8 meals per month calculated for 2022.

Sediment-connected Potentially Toxic Element Contamination and Phytoremediation Potential of Native Aquatic Macrophytes along the Jajrood River, Tehran Province, Iran

This study was conducted to analyze Cu, Fe, and Pb contamination in sediments and also phytoremediation ability of bulrush (Typha Latifolia) and one-rowed water-cress (Nasturtium microphyllum) along the Jajrood River, Iran in 2022. In so doing, a total of 60 sediment and macrophyte samples were collected from four sites. The contents of the analyzed elements were determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES). Also, the values of pollution index (PI), pollution load index (PLI), bioconcentration factor (BCF), bioaccumulation factor (BAF), transfer factor (TF) and metal accumulation index (MAI) were calculated. The results demonstrated that the average contents of Cu, Fe, and Pb were lower than those in the background, which presumably demonstrated natural sources of these metals. The greatest concentrations of analyzed elements for all the sediment and macrophyte samples were observed in specimens collected from S4 located at the end of the river, indicating the impact of anthropogenic entries from upstream areas on elemental accumulation in downstream section of the river. The values of PI reflected slight contamination. The higher BCF and lower translocation TF values of Fe and Pb in T. Latifolia and also Cu in N. microphyllum imply that these species could be suitable for their phytostabilization of above-mentioned elements from the sediment. This study provides evidenceas to the efficiency of T. Latifolia and N. microphyllum in bioremediation of Cu, Fe, and Pb in contaminated aquatic environments.

Considerations for environmental biogeochemistry and food security for aquaculture around Lake Victoria, Kenya

The impact of population expansion through economic growth and development has been identified as one of the key drivers of both water and sediment contamination from potentially harmful elements (PHEs). This presents a major hazard not only to aquatic ecosystems but local riparian communities and beyond who rely heavily on this natural resource for drinking water and fish-a valuable source of dietary micronutrients and protein. The present study measured biogeochemical concentration of PHEs in water, sediment and fish from locations pooled into four zones within Winam Gulf and Lake Victoria area of Kenya. Captured fish were used as a sentinel receptor of lake health to evaluate potential risks to fisheries and aquaculture food security. In water, concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu) and lead (Pb) were observed above the United States Environmental Protection Agency (US EPA) maximum contamination level drinking water guidelines (MCL), with aluminium (Al) observed above the Aquatic Life Criteria in all four zones. Similarly, sediment concentrations in all four zones exceeded the US EPA Effects range low (ERL) threshold guidelines for Cu, nickel (Ni), zinc (Zn) and Pb, with Cu, Zn and Pb classed at moderate contamination levels using the contamination factor. Fish tissue concentrations from the four zones were calculated using recommended daily intakes (RDI) and for PHEs as provisional maximum tolerable intakes (PMTIs) and indicated most macro- and micronutrients were at or below 10% RDI from aquaculture and wild fish, with Se indicating a greater RDI (16-29%) in all the zones. Contributions of PHEs to PMTIs were below threshold guidelines for both aquaculture and wild fish with only Cd, Cr and Pb levels being above the PMTI thresholds. There is a need to assess the long-term effects of persistent anthropogenic PHE input into Winam Gulf and the wider Lake Victoria basin. Continued monitoring of PHEs using both historical and more recent data will enable future management policies to be implemented through improved mitigation strategies to reduce their impact on water quality, fish health and subsequent human health.

Contribution of pollution gradient to the sediment microbiome and potential pathogens in urban streams draining into Lake Victoria (Kenya)

In sub-Saharan Africa (SSA), urban rivers/streams have long been subjected to anthropogenic pollution caused by urbanization, resulting in significantly altered chemical and biological properties of surface water and sediments. However, little is known about the diversity and structure of river microbial community composition and pathogens, as well as how they respond to anthropogenic inputs. High-throughput 16S rRNA amplicon sequencing and PICRUSt predictive function profiling were used in this study to conduct a comprehensive analysis of the spatial bacterial distribution and metabolic functions in sediment of two urban streams (Kisat and Auji) flowing through Kisumu City, Kenya. Results revealed that sediment samples from the highly urbanized mid and lower stream catchment zones of both streams had significantly higher levels of total organic carbon (TOC), total nitrogen (TN), total phosphorous (TP) than the less urbanized upper catchment zone, and were severely polluted with toxic heavy metals lead (Pb), cadmium (Cd), and copper (Cu). Differential distribution of Actinobacteria, Proteobacteria, Chloroflexi, and Verrucomicrobia in sediment bacterial composition was detected along stream catchment zones. The polluted mid and lower catchment zones were rich in Actinobacteria and Proteobacteria, as well as a variety of potential pathogenic taxa such as Corynebacterium, Staphylococcus, Cutibacterium, Turicella, Acinetobacter, and Micrococcus, as well as enteric bacteria such as Faecalibacterium, Shewanella, Escherichia, Klebsiella, Enterococcus, Prevotella, Legionella, Vibrio and Salmonella. Furthermore, PICRUSt metabolic inference analysis revealed an increasing enrichment in the sediments of genes associated with carbon and nitrogen metabolism, disease pathogenesis, and virulence. Environmental factors (TOC, Pb, Cd, TN, pH) and geographical distance as significant drivers of sediment bacterial community assembly, with the environmental selection to play a dominant role. In polluted river catchment zone sediment samples, Pb content was the most influential sediment property, followed by TOC and Cd content. Given the predicted increase in urbanization in SSA, further alteration of surface water and sediment microbiome due to urban river pollution is unavoidable, with potential long-term effects on ecosystem function and potential health hazards. As a result, this study provides valuable information for ecological risk assessment and management of urban rivers impacted by diffuse and point source anthropogenic inputs, which is critical for future proactive and sustainable urban waste management, monitoring, and water pollution control in low-income countries.

Effects of different water conditions on the cadmium hyperaccumulation efficiency of Rorippa sylvestris (L.) Besser and Rorippa amphibia Besser

Increasing the translocation and accumulation of cadmium (Cd) in Cd hyperaccumulator is an important technology to improve the phytoremediation efficiency of Cd-contaminated soil. In order to investigate the effects of different water conditions on the growth and Cd accumulation ability of Cd hyperaccumulators Rorippa sylvestris (L.) Besser and Rorippa amphibia Besser in Cd-polluted soil, clone seedlings of them were transplanted into pots filled with 50 mg kg^-1 Cd-contaminated soil and cultured with water conditions of soil relative water content (RWC) 35%, 55%, 75%, 95%, and flooding respectively. The results showed the following: with the increase of RWC, the height of R. sylvestris and R. amphibia increased gradually, the dry biomass of shoot and whole plant increased and reached the maximum in 95% and then decreased in flooding; the Cd concentrations in shoots of R. sylvestris and R. amphibia were more than 100 mg kg^-1 except for 35% and flooding; Cd bioconcentration factors (BCFs) of R. amphibia reached the maximum of 3.8870 in 75% and R. sylvestris reached the maximum of 3.2330 in 95%; sufficient water resulted in the decrease of photosynthetic rate due to more Cd accumulation. However, under flooding condition, because of the decrease of Cd bioavailability in soil, the accumulation of Cd in shoots declined and the net photosynthetic rate (P_n) enhanced slightly.

Rat Hepatocytes Mitigate Cadmium Toxicity by Forming Annular Gap Junctions and Degrading Them via Endosome-Lysosome Pathway

Gap junction protein connexin 43 (Cx43) plays a critical role in gap junction communication in rat hepatocytes. However, those located between hepatocytes are easily internalized following exposure to poisons. Herein, we investigated the potential of buffalo rat liver 3A (BRL 3A) cells to generate annular gap junctions (AGJs) proficient at alleviating cadmium (Cd) cytotoxic injury through degradation via an endosome-lysosome pathway. Our results showed that Cd-induced damage of liver microtubules promoted Cx43 internalization and increased Cx43 phosphorylation at Ser373 site. Furthermore, we established that Cd induced AGJs generation in BRL 3A cells, and AGJs were subsequently degraded through the endosome-lysosome pathway. Overall, our results suggested that Cx43 internalization and the generation of AGJs were cellular protective mechanisms to alleviate Cd toxicity in rat hepatocytes.

A comprehensive review of heavy metal pollution in the coastal areas of Bangladesh: abundance, bioaccumulation, health implications, and challenges

The coastal zone of Bangladesh, with a population density of 1278 people per square kilometer, is under serious threat due to heavy metal pollution. To date, many studies have been conducted on the heavy metal contamination in soils, water, aquatic animals, and plants in the coastal zone of Bangladesh; however, the available information is dispersed. In this study, previous findings on the contamination levels, distributions, risks, and sources of heavy metals in sediments and organisms were summarized for the first time to present the overall status of heavy metal pollution along coastal regions. Earlier research found that the concentrations of various heavy metals (HMs), particularly Co, Cd, Pb, Cu, Cr, Mn, Fe, and Ni in water, sediment, and fish in most coastal locations, were above their permissible limits. High concentrations of HMs were observed in sediments and water, like Cr of 55 mg/kg and 86.93 mg/l in the ship-breaking areas and Karnaphuli River, respectively, in coastal regions of Bangladesh. Heavy metals severely contaminated the Karnaphuli River estuary and ship-breaking area on the Sitakundu coast, where sediments were the ultimate sink of high concentrations of metals. Sedentary or bottom-dwelling organisms like gastropods and shrimp had higher levels of heavy metals than other organisms. As a result, the modified PRISMA review method was used to look at the critical research gap about heavy metal pollution in Bangladesh's coastal areas by analyzing the current research trends and bottlenecks.

Assessing the Association of Element Imbalances With Arsenism and the Potential Application Value of Rosa roxburghii Tratt Juice

Endemic arsenism caused by coal burning is a unique type of biogeochemical disease that only exists in China, and it is also a disease of element imbalances. Previous studies have shown that element imbalances are involved in the pathogenesis of arsenic; however, the interaction between the various elements and effective preventive measures have not been fully studied. This study first conducted a cross-sectional study of a total of 365 participants. The results showed that arsenic exposure can increase the content of elements (Al, As, Fe, Hg, K, and Na) in the hair (p < 0.05), but the content of other elements (Ca, Co, Cu, Mn, Mo, P, Se, Sr, V, and Zn) was significantly decreased (p < 0.05). Also, the high level of As, Fe, and Pb and the low level of Se can increase the risk of arsenism (p < 0.05). Further study found that the combined exposure of Fe–As and Pb–As can increase the risk of arsenism, but the combined exposure of Se–As can reduce the risk of arsenism (p < 0.05). In particular, a randomized, controlled, double-blind intervention study reveals that Rosa roxburghii Tratt juice (RRT) can reverse the abovementioned element imbalances (the high level of Al, As, and Fe and the low level of Cu, Mn, Se, Sr, and Zn) caused by arsenic (p < 0.05). Our study provides some limited evidence that the element imbalances (the high level of As, Fe, and Pb and the low level of Se) are the risk factors for the occurrences of arsenism. The second major finding was that RRT can regulate the element imbalances, which is expected to improve arsenism. This study provides a scientific basis for further understanding a possible traditional Chinese health food, RRT, as a more effective detoxication of arsenism.

Phytoremediation of heavy metals and total petroleum hydrocarbon and nutrients enhancement of Typha latifolia in petroleum secondary effluent for biomass growth

Phytoremediation is an innovative tool which can be used for the treatment of industrial and agricultural wastewater. Typha latifolia (T. latifolia) is an aquatic plant used for phytoremediation of heavy metals (HMs) like cadmium (Cd), cobalt (Co), manganese (Mn), and TPH (total petroleum hydrocarbon) for the treatment of petroleum secondary effluent (PSE). During this experiment, the growth of T. latifolia in biomass, nutrient concentrations, and heavy metals were studied. The results indicated that T. latifolia was more tolerant to Cd, Co, and Mn due to its transfer index (TI) which was found to be greater than 2.9. The enrichment coefficients of the metals, Cd and Co present in the root were found to be higher than 3.31 to 2.56 and 5.35 to 3.55, respectively unlike the stem of T. latifolia. But, the enrichment coefficient of Mn was found to be 1.98 which was expected to be 3.51 at 75%. Similarly, the enrichment coefficients of all the metals, except for Co, in roots of T. latifolia were higher than 5.36. (TI) for Co (2.95) and Mn (2.55) which is better as compared to the enrichment coefficients of Cd (2.35) and TPH (3.45) in PSE. Thus, there is a possibility that PSE could be a source of important nutrients.

Spatial distributions and risk assessments of nutrients and heavy metalsin sediments from an impounded lake of China's South-to-NorthWater Diversion Project

The high-density distribution patterns of the nutrients (C, N, P) and heavy metals (Fe, Mg, Zn, Cr, Pb, Ni, Cu, Cd) in sediments from Lake Luoma, as well as their pollution status and ecological risks, were characterized, to comprehensively understand potential environmental impacts of inter-basin water transfers. TN, TP, and OM were measured from 162.50 to 4360.00 mg kg-1, 165.00 to 1302.50 mg kg-1, and 1% to 13%, which were primarily accumulated in the eastern, northwest, and western regions, respectively. A total of 8 heavy metals except for Fe generally exhibited a similar distribution pattern, reflected by a gradually decreasing trend from northwest to southeast region. The averaged concentrations of heavy metals decreased as follows: Fe > Mg > Zn > Cr > Pb > Ni > Cu > Cd. Comprehensive pollution risk assessments indicated that the sediments of Lake Luoma were heavily polluted by TN, OM, and Cd. Multivariate statistical analyses demonstrated that the main pollution sources of Zn and Ni were fertilizers and pesticides, Cd and Pb are mainly derived from industrial wastewater, and TN and OM may come from natural and agricultural factors. This research can provide data support for water pollution control and drinking water diversion management in the Lake Luoma basin.

Parasite diversity of introduced fish Lates niloticus, Oreochromis niloticus and endemic Haplochromis spp. of Lake Victoria, Kenya

This study reports on the status of metazoan fish parasites in Lake Victoria following the establishment of introduced Lates niloticus (Latidae) and Oreochromis niloticus (Cichlidae) and changes in environmental quality. For this study, 412 fish specimens were examined for parasites: 103 L. niloticus, 165 O. niloticus, 82 Haplochromis piceatus and 62 H. humilior (endemic cichlids). In total, 25 parasite taxa were identified: Lates niloticus (6), O. niloticus (19) and Haplochromis spp. (13). The myxosporean Henneguya ghaffari, prevalence (P) = 79% and the monogenean Diplectanum lacustris (P = 34%), were the dominant parasites on L. niloticus. Myxobolus sp. (P = 44%) was dominant on O. niloticus while for the haplochromines, metacercariae of 'Neascus' sp. (Diplostomidae) was dominant (P = 37%). Contrary to reports of high diversity of monogeneans on endemic species, the haplochromines harboured only Cichlidogyrus gillardinae (P = 6.9%). Oreochromis niloticus harboured seven monogenean species: Cichlidogyrus sclerosus, C. halli, C. tilapiae, C. quaestio, Scutogyrus longicornis, Gyrodactylus cichlidarum and G. malalai-they appear to have been co-introduced with the fish. Cichlidogyrus gillardinae, C. quaestio, G. malalai and the acanthocephalan Acanthogyrus (Acathosentis) tilapiae are recorded for the first time in Lake Victoria, representing new geographical records. Presence of A. (A) tilapiae in Haplochromis spp. indicates possible spillover from O. niloticus. Low prevalence and diversity of monogeneans, crustaceans and glochidia on the fish corresponded with increased pollution in the lake. Overall, changing environmental conditions and introductions of fish species have contributed to parasite community changes in Lake Victoria.

Integration of physical, geochemical and biological analyses as a strategy for coastal lagoon biomonitoring

Coastal lagoons are complex environments threatened by natural and anthropogenic stressors. Here, we tested the effectiveness of combining physical, geochemical and chemical measurements with biomarker data obtained in field-exposed marine mussels (Mytilus galloprovincialis) as a biomonitoring strategy for a highly pressured lagoon (Pialassa Baiona, Ravenna, Italy). Data showed a spatial trend of sediment contamination by Hg, Pt, Au, Ag, Mo, Re, Cd, Pd and Zn. Local conditions of high water temperature/low conductivity were detected among selected sites. After a 30-day in situ exposure, Ag and Hg were the most bioaccumulated elements (10 and 5 folds, respectively) in mussels followed by Sb, Al, Ti and Fe. Decreased survival, lysosomal dysfunctions, increased metallothionein content and peroxisome proliferation were observed in mussels in relation to metal spatial distribution and physico-chemical fluctuations. Overall, this study provides a further confirmation of the role of biomonitoring to reliably assess the environmental quality of highly pressured lagoons.

Quantitative assessment of metal contamination and associated pollution risk in sediments from the Mara River in Tanzania

For most rivers in sub-Saharan Africa, information about pollution indices related to sediments is sparse. Sedimentological research of rivers that empty into Lake Victoria is highly patchy and wide apart. The present study determined the levels and associated risk of As, Cd, Cr, Hg, and Pb in sediments collected from four different sites along the Mara River that empties into Lake Victoria in Tanzania. Samples were collected in the dry and rainy months in 2019. Pollution indices, namely geo-accumulation index (I_geo), enrichment factor (EF), contamination factor (CF), modified contamination degree (mCd), pollution load index (PLI), potential ecological risk factor (E_rⁱ), and potential ecological risk index (RI) were used to evaluate the influence of heavy metal contamination in sediments. Dry month mean concentrations, in milligram per kilogram, of heavy metals were as follows: As (11.04 ± 0.13), Cr (1.02 ± 0.29), Cd (0.43 ± 0.05), and Hg (0.01) in the dry month. Respective sediment heavy metal concentrations for the rainy month were 22.22 ± 0.05 mg As/kg, 3.84 ± 0.34 mg Pb/kg, 1.53 ± 0.15 mg Cd/kg, 1.43 mg Cr/kg, and 0.03 mg Hg/kg. Generally, the risk indices showed high values in the rainy month and low values in the dry month, especially for As and Cd-an indication of anthropogenic influence. Correlation coefficient analysis for Pb and Cd showed a strong positive correlation (r = 0.99, p < 0.01)-this may suggest a similar source or similar transport behavior. Special attention needs to be paid with regard to rainy season As and Cd enrichment in the study area.

Diversity of digenean trematode larvae in snails from Lake Victoria, Kenya: First reports and bioindicative aspects

This study investigated the occurrence of digenean trematode larvae in snails from the Kenyan part of Lake Victoria. The survey included caenogastropod snails that have received less focus in parasitological studies in Africa: their trematodes are largely unknown. Out of 1145 snail specimens, 149 (13.0%) were infected with Digenea. The highest prevalence (P) was recorded in Melanoides tuberculata (64.5%), followed by Pila ovata (15.4%), Radix natalensis (9.5%), Bulinus ugandae (9.1%), Bellamya unicolor (8.9%), Biomphalaria pfeifferi (7.3%) and Biomphalaria sudanica (4.4%). Morphological and molecular analyses revealed 17 digenean species. Contrary to reports of low diversity of Digenea in caenogastropods, P. ovata harboured 8 species - at least twice as many as in each of the pulmonates. The following taxa are reported for the first time in the Lake Victoria region: Haplorchis pumilio, Thapariella prudhoei, Nudacotyle sp., Renicola sp. and Bolbophorus sp. An unknown cercaria belonging to the genus Haematoloechus is reported from P. ovata: a xiphidiocercaria possessing a long sword-shaped stylet (47-71 µm) which does not match any available literature records. From this study, H. pumilio from M. tuberculata (P = 69.4%), Fasciola gigantica from R. natalensis (P = 1.9%) and Bolbophorus sp. from Bu. ugandae (P = 4.6%) are species of veterinary or medical importance. Snails from the study site with little direct anthropogenic influence had the highest prevalence and diversity of digenean larvae, indicating that environmental conditions influence trematode occurrence.

Trace Elements in Crustaceans, Mollusks and Fish in the Kenyan Part of Lake Victoria: Bioaccumulation, Bioindication and Health Risk Analysis

This is the first comprehensive report on the accumulation of Cr, Ni, As, and Ag in the fish species Nile tilapia Oreochromis niloticus and Nile perch Lates niloticus from Lake Victoria, complemented with recent data on Cu, Zn, Cd, and Pb. This also is the first report on Cr, Ni, As, and Ag levels in invertebrates: the shrimp Caridina nilotica, gastropod Pila ovata, and bivalve Mutela bourguignati. The study was conducted at five sites in the Kenyan part of Lake Victoria: four sites in Winam Gulf influenced by various anthropogenic pressures, including a site near Kisumu City, and one in the main lake, with lesser direct anthropogenic influence. Apart from Cu and Ag, which were highest in O. niloticus liver, the invertebrates had higher levels of trace elements than fish. Contamination of the gulf with trace elements was best mirrored by the invertebrates, whose mobility is limited; they accumulated Cr, Cd, Ag, and Pb corresponding to the levels in the surface sediment. The accumulation of trace elements in fish species and their bioindicative potential corresponded to their habitats and feeding behaviour. The tissue contents of most trace elements were higher in the inshore-dwelling, omnivorous O. niloticus compared to the pelagic, piscivorous L. niloticus. Cu (465 ± 689 mg/kg dw) and Ag (3.45 ± 1.49 mg/kg dw) in the liver of O. niloticus were up to 10 and 119 times higher than in L. niloticus, respectively. Oreochromis niloticus therefore has bioindicative potential for Cu and Ag contamination. Both the invertebrates and fish showed positive correlations between Cu and Ag concentrations, indicating similar source and/or uptake route. The target hazard quotients (THQ) show that there is no human health risk associated with the consumption of these fish. However, the levels of Zn, Cd, and Pb in P. ovata surpassed maximum food safety limits and are hence potentially unsafe for human consumption.