Investigating the effect of Eh and pH on binding forms of Co, Cu, and Pb in wetland sediments from Zambia.

This study investigated binding forms of cobalt (Co), copper (Cu), and lead (Pb) in 28 sediment samples from inlet to outlet of three Zambian wetlands receiving mining effluents. Use was made of a modified Tessier metal binding fractions procedure. Due to storage artefacts, the original aim of investigating the effects of redox potential (Eh) changes, starting from extremely low Eh, was suspended. Instead, use was made of the new, not often explored opportunity for replicate sample division into three categories of varying redox potential and pH. Additionally, in line with the original research aim, two sediments from each wetland were investigated for their response to increasing Eh. The results showed overall high trace metal contents, with a need for remedial actions for Co and Cu in the first, Cu in the second, and Pb in the third wetland. Rather independent of Eh and pH, Co was often found in the residual fraction (F5), as well as in the oxidizable (F4) and reducible (F3) fraction. Cu was generally dominant in F5 and F4 fractions, with low F3 prevalence, indicating a high organic matter affinity. Pb distribution among binding forms showed small variations within and across wetlands, F5, F4, and F3 fractions dominating. In the above observations, statistical analysis showed that, among the 28 sediment samples across wetlands, the influence of Eh and pH on binding forms were generally found to be not significant, being 'overruled' by other sedimentological factors. With increasing Eh, the decrease in the oxidizable (F4) fraction was smaller than expected in eight of 18 tests. The Risk Assessment Code (RAC) method, based on the exchangeable fraction (F1) plus carbonate fraction (F2), showed that some sediments turned from "unsafe" to "safe," and vice versa, with increasing Eh. The "total metals method" does not show bioavailability, whereas RAC does not use the metal contents. Thus, the two methods should be used together to improve the prediction of potential toxicity.

Distribution of the heavy metals Co, Cu, and Pb in sediments and Typha spp. And Phragmites mauritianus in three Zambian wetlands.

Zambia has been mining cobalt (Co), copper (Cu), and lead (Pb) for over a century, with discharges entering wetlands without investigations on the level of sediment pollution and how to solve it. This present study investigated: 1) the extent to which Co, Cu, and Pb that enter through mining wastewater were distributed in the sediment of three wetlands (Uchi, Mufulira, and Kabwe) in Zambia and 2) the accumulation and distribution of the heavy metals in two emergent wetland plants, Phragmites mauritianus, and Typha spp. in order to evaluate their potential for phytoremediation of metals. Samples from three sections (inlet, middle section and outlet) of each wetland were analyzed for the heavy metal contents. Sediment contents of Co and Cu were significantly higher in the Uchi wetland than in the other two, while Pb was significantly higher in the Kabwe wetland. Cu in all the wetlands were found to be at levels considered a threat to aquatic life, with Pb contents in Kabwe a risk to human health. Both P. mauritianus and Typha spp acted as excluder species for Co, Cu, and Pb, showing bioaccumulation factor (BAF) < 1 and Translocation factor (TF) < 1 for all wetlands. As neither species accumulated cellularly toxic concentrations of Co, Cu, and Pb, they could grow in the contaminated sediments. Currently, methods used to solve historic mining impacts in Zambian wetlands aim at improving water flow and reducing flooding without attending to the heavy metal contents of the sediments. From this study, P. mauritianus and Typha spp. provide the potential for phytostabilisation to settle and contain polluted sediments.

Investigating Co, Cu, and Pb retention and remobilization after drying and rewetting treatments in greenhouse laboratory-scale constructed treatments with and without Typha angustifolia, and connected phytoremediation potential.

There is critical concern over heavy metals because they are biotoxins. The best management option is elimination or at least minimization of effluence into the environment, but in several regions, mining wastewater or acid mine drainage (AMD) effluence into natural wetlands has continued. The ability of wetlands to attenuate heavy metals in mining wastewater and AMD has led to natural wetlands being used as recipients of these effluents in many parts of the world. Ten greenhouse-based laboratory-scale constructed wetlands (GLCW) were set up at IHE-Delft Institute for Water Education to understand the mechanisms and fate of heavy metals in three Zambian wetlands in attenuation of Co, Cu, and Pb. These were operated as Free Water Surface Constructed Wetlands (FWS-CWs). The principal investigations compared how vegetated and unvegetated microcosm artificial wetlands retained controlled additions of heavy metals and the effect of drying and rewetting on that. The potential for phytoremediation using Typha angustifolia was also investigated. Typha angustifolia was planted in three vegetated and compared with one unvegetated treatment. Treatments A, B, and, the investigated, Treatment D received synthetic wastewater containing Co, Cu, and Pb, while a control, Treatment C, received tap water. Water samples were taken throughout the experiment, and sediment samples collected after the first flushing and before drying. Samples of T. angustifolia were taken before drying the wetlands. Analyses for Co, Cu, and Pb were made in the water and sediment, and in roots, stems and leaves of plant samples. The unvegetated Dutch sediments GLCWs removed more Co from wastewater (52%) than the vegetated Dutch and Zambian sediments GLCWs (13% and -4%, respectively). There was a similar removal of Cu among the GLCWs receiving wastewater (81%-87%). The removal of Pb was significantly higher in the vegetated Dutch sediment GLCWs than the unvegetated Dutch sediments GLCWs, (89% and 72%, respectively). It was concluded that a hectare of the vegetated Zambian sediments with similar design parameters of 50 mg/m2.day for Co, Cu, and Pb used in the experiment would on average retain 83 g/day of Co, and 417 g/day of both Cu and Pb. After drying, Co, Cu, and Pb washed out on the first day of rewetting. The washout after that took only a few days. How long the metals washed out of the GLCWs was in order Co > Cu > Pb. T. angustifolia could neither be classified as an accumulator nor an excluder species because the concentrations of Co, Cu, and Pb in the sediments and T. angustifolia were below phytotoxic levels mainly due to a short running period of the experiment.

Estimating Total Nitrogen and Phosphorus Losses in a Data-Poor Ethiopian Catchment.

Selecting a suitable model for a water quality study depends on the objectives, the characteristics of the study area, and the availability, appropriateness, and quality of data. In areas where in-stream chemical and hydrological data are limited but where estimates of nutrient loads are needed to guide management, it is necessary to apply more generalized models that make few assumptions about underlying processes. This paper presents the selection and application of a model to estimate total nitrogen (TN) and total phosphorus (TP) loads in two semiarid and adjacent catchments exposed to pollution risk in north-central Ethiopia. Using specific criteria to assess model suitability resulted in the use of the Pollution Load (PLOAD) model. The model relies on estimates of nutrient loads from point sources such as industries and export coefficients of land use, and it is calibrated using measured TN and TP loads from the catchments. The performance of the calibrated PLOAD model was increased, reducing the sum of errors by 89 and 5% for the TN and TP loads, respectively. The results were validated using independent field data. Next, two scenarios were evaluated: (i) use of riparian buffer strips, and (ii) enhanced treatment of industrial effluents. The model estimated that combined use of the two scenarios could reduce TN and TP loads by nearly 50%. Our modeling is particularly useful for initial characterization of nutrient pollution in catchments. With careful calibration and validation, PLOAD model can serve an important role in planning industrial and agricultural development in data-poor areas.

Assessment of DDT, HCH and PAH contamination and associated ecotoxicological risks in surface sediments of coastal Tema Harbour (Ghana).

This study assessed DDTs, HCHs and PAHs contamination in sediments from the Tema Harbour (Ghana) and the associated ecotoxicological risks. The results showed widespread DDTs, HCHs and PAHs contamination in the harbour sediments with mean concentrations ranging from 6.0-12.8, 2.8-12.7 and 2750-5130µg·kg-1d·w, respectively. The silt-clay and total organic carbon contents of the sediments poorly correlated with the pollutant concentrations. DDTs and HCHs contamination relate to past use of DDT and lindane, which under the anoxic harbour conditions resulted in disproportionately higher concentrations of p,p'-DDD and γ-HCH in the sediments. No conclusion could be drawn on the sources of PAHs as either petrogenic or pyrogenic. The pollutant concentrations in the harbour sediments, particularly γ-HCH, may pose high ecotoxicological risks. In comparison to a previous study, this study indicates there has been a considerable reduction in PAH contamination in the Tema Harbour since the last major oil spill in 2007.

Occupational exposure to pesticides: blood cholinesterase activity in a farming community in Ghana.

A survey was undertaken to establish the extent of pesticide exposure in a farming community. Cholinesterase (ChE) activity in whole blood was used as a marker for assessing exposure to pesticides. Complete data were gathered for 63 farmers at Akumadan (exposed) and 58 control subjects at Tono, both prominent vegetable-farming communities in Ghana, by means of a questionnaire and blood cholinesterase analyses (acetylcholine assay). Although whole-blood ChE was significantly lower in the exposed than the control participants, it was not significantly correlated with either confounders of age, sex, body weight, and height or high-risks practices. The high-risks practices revealed during the survey included lack of use of personal protective clothing, short reentry intervals, and wrong direction of spraying of pesticides by hand or knapsack sprayer. About 97% of exposed participants had experienced symptoms attributable to pesticide exposure. The frequent symptoms were reported as weakness and headache. There is the need to review safety precautions in the use and application of pesticides in Ghana.

The impact of agricultural runoff on the quality of two streams in vegetable farm areas in Ghana.

A study of two small streams at Akumadan and Tono, Ghana, was undertaken during the rain and dry season periods between February 2005 and January 2006 to investigate the impact of vegetable field runoff on their quality. In each stream we compared the concentration of current-use pesticides in one site immediately upstream of a vegetable field with a second site immediately downstream. Only trace concentrations of endosulfan and chlorpyrifos were detected at both sites in both streams in the dry season. In the wet season, rain-induced runoff transported pesticides into downstream stretches of the streams. Average peak levels in the streams themselves were 0.07 microg L(-1) endosulfan, 0.02 microg L(-1) chlorpyrifos (the Akumadan stream); 0.04 microg L(-1) endosulfan, 0.02 microg L(-1) chlorpyrifos (the Tono stream). Respective average pesticide levels associated with streambed sediment were 1.34 and 0.32 microg kg(-1) (the Akumadan stream), and 0.92 and 0.84 microg kg(-1) (the Tono stream). Further investigations are needed to establish the potential endosulfan and chlorpyrifos effects on aquatic invertebrate and fish in these streams. Meanwhile measures should be undertaken to reduce the input of these chemicals via runoff.

Accumulation of persistent organochlorine contaminants in milk and serum of farmers from Ghana.

In the present study, the concentrations of persistent organochlorine (OC) pesticides such as dichlorodiphenyltrichloroethane and its metabolites (DDTs), hexachlorocyclohexane isomers (HCHs), hexachlorobenzene (HCB) and dieldrin in pooled samples of human breast milk (n=109), and serum (n=115) from vegetable farmers in Ghana, during 2005, were determined. Gas chromatography with mass spectrometry was used to quantify residue levels on a lipid basis of the OCs. The pattern of OCs in human fluid showed that DDTs was consistently the prevalent OC in milk and blood. The levels of DDTs, HCHs, and dieldrin in the breast milk samples were found to correlate positively with age of the milk sample donors (r(s)=0.606, 0.770, and 0.540, respectively). When blood serum levels of the OCs were compared between male and female farmers, no pronounced relationship for HCHs and HCB (p>0.05) was observed. However, DDTs and dieldrin residues were significantly higher (p<0.05) in males than in females. There was association between breast milk and serum residues. When daily intakes of DDTs and HCHs to infants through human breast milk were estimated, some individual farmers (in the case of DDTs) and all farmers (in the case of HCHs) accumulated OCs in breast milk above the threshold (tolerable daily intake, TDI, guidelines proposed by Health Canada) for adverse effects, which may raise concern on children health.

Dissipation of endosulfan in field-grown tomato (Lycopersicon esculentum) and cropped soil at Akumadan, Ghana.

The dissipation and persistence of endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin 3-oxide) applied to field-grown tomato (Lycopersicon esculentum) were studied at a vegetable-growing location in Ghana. Plant tissue samples and cropped soil collected at 2 h-14 days and 8 h-112 days, respectively, after application, were analyzed by gas chromatography-electron capture detection (63Ni) to determine the content and dissipation rate of endosulfan isomers (alpha- and beta-endosulfan) and the major metabolite, endosulfan sulfate. After two foliar applications of commercial endosulfan at 500 g of active ingredient/hectare, the first-order reaction kinetic was confirmed to describe the dissipation of endosulfan residues in tomato foliage and cropped soil. However, functions that best fit the experimental data were the biphasic process for foliage and the monophasic process for cropped soil. Calculated DT 50 and DT 90 values for endosulfan residues in cropped soil were not significantly (p<0.05) different for each of the two isomers.

Farmer perceptions and pesticide use practices in vegetable production in Ghana.

As an initial part of a programme aimed at promoting safe and sound agricultural practices in Ghana, a study was made of farmers' perceptions of pesticides for use and application in vegetable production, using a small survey of 137 farmers who applied pesticides. Field surveys, interviews, questionnaires and analytical games were used to obtain information on the type, scope and extent of use of pesticides, farmers' knowledge of pesticides, and their perceptions about the chemicals' potential for harm. Data from this sample of farmers were used to describe the status of use of pesticides in vegetable cultivation in Ghana. Using chi2 tests, associations between farmers' age and possible pesticide poisoning symptoms, their farm size and method of spraying pesticides, and their perception of pesticide hazard and its perceived effectiveness against pests were also examined. The survey showed that knapsack sprayers were the most widely used type of equipment for spraying pesticides. However, on large-scale vegetable farms of 6-10 acres, motorised sprayers were also used. Various inappropriate practices in the handling and use of pesticides caused possible poisoning symptoms among those farmers who generally did not wear protective clothing. Younger farmers (<45 years of age) were the most vulnerable group, probably because they did more spraying than older farmers (>45 years of age). Farmers did not necessarily associate hazardous pesticides with better pest control. The introduction of well-targeted training programmes for farmers on the need for and safe use of pesticides is advocated.