Lake Victoria, East Africa, has been the site of many recent studies measuring mercury (Hg) concentrations in water, fish, sediment, soil, and humans. Most of these studies were motivated by concerns about Hg contamination from processing of gold ore on the southern shores. Total Hg (THg) concentrations in fish were usually below permissible World Health Organization (WHO) concentrations and international marketing limits and do not threaten the lucrative export industry. Nile perch 3–10 kg and most >10 kg had THg concentrations above the WHO threshold concentrations for at-risk groups (200 ng/g). Elevated THg concentrations in large Nile perch are not of major concern because Nile perch are rarely consumed by the people living on Lake Victoria and very large Nile perch are becoming increasingly rare in catches. Water THg concentrations were below Canadian drinking water guidelines but were elevated relative to those in the northern Great Lakes. Sediment and soil THg concentrations were within international guidelines and are comparable to those in northern latitudes but are lower than those in the Amazon basin. Biomass burnings and soil erosion are estimated to be the major sources of THg for the lake and probably constitute a larger source of THg than gold mining in Tanzania. THg concentrations in urine and hair from human volunteers indicate that while gold miners and frequent skin-bleaching cream users are at risk of inorganic mercury poisoning, the rest of the population, including fishermen, is not. Human exposure assessments demonstrated that fish consumption and soil geophagy constitute major sources of THg for humans, but the total estimated daily intake of THg was below the Health Canada tolerable daily intake (TDI) limits. The use of beauty creams containing high inorganic Hg concentrations, however, caused the estimated THg exposure to exceed the TDI. The high THg content in the hair of regular cream users supports this assessment. The nutritional benefits of fish and soil geophagy outweigh the risk of THg poisoning. Still, due to the importance of those natural items as a THg source to humans, as well as the changing nature of Lake Victoria, regular monitoring and risk assessments need to be carried out in the Lake Victoria catchment.

https://ap.smu.ca/~lcampbel/CampbelletalJETH2003.pdf

A review of mercury in Lake Victoria, East Africa: implications for human and ecosystem health.

In agricultural landscapes, rural and municipal residents can be exposed to agricultural pesticides either directly during crop applications or indirectly in air, water, or food. In the northern Great Plains of the United States and Canada, pesticides have been detected in atmospheric samples, in surface and groundwaters, and in a variety of food products. Studies in the United States (Garry et al. 1996), Spain (Garcia-Rodriguez et al. 1996), and New Zealand (Hanify et al. 1981) have shown that environmental exposure to agricultural chemicals is associated with increases in human health anomalies. These include reduced stamina, gross and fine eye–hand coordination, and cognitive abilities in children (Guillette et al. 1998); an increased incidence of human birth malformations (Garry et al. 1996; Hanify et al. 1981; Schreinemachers 2003); and cryptorchidism in male children (Garcia-Rodriguez et al. 1996).

Pesticide exposure through potable water has become a concern. Using a statewide survey of 856 Iowa municipal drinking water supplies, Munger et al. (1997) compared the rate of intrauterine growth retardation in births by women whose drinking water contained higher levels of herbicides [atrazine, cyanazine, metolachlor, and (2,4-dichloro-phenoxy)acetic acid (2,4-D)] with that in births by women using other sources of drinking water. The authors concluded that atrazine, metolachlor, and cyanazine were each significant predictors of intrauterine growth retardation and that areas with drinking water containing higher herbicide concentrations had higher rates of intrauterine growth retardation than nearby communities with other sources of drinking water.

In the northern Great Plains of Canada and the United States, drinking water sources include groundwater and large rivers. However, because of inadequate volume or unsuitability of groundwater because of high mineral content, residents of some smaller communities derive their drinking water from small reservoirs with drainage areas imbedded in agricultural landscapes. In a 3-year study, Cessna and Elliott (2004) monitored prairie farm dugouts (constructed ponds) in Saskatchewan for several herbicides used extensively in crop production on the Canadian prairies. Two of these small reservoirs were used by the farm families for drinking water and household water. Herbicides detected in these dugouts were those expected from an agricultural landscape dominated by cereal and oilseed production and included 2,4-D, diclofop, bromoxynil, (2-chloro-4-methylphenoxy)acetic acid (MCPA), triallate, dichlorprop, dicamba, clopyralid, and tri-fluralin. Consequently, we hypothesized that rural populations obtaining drinking water from catchments that are predominantly crop lands may be exposed to relatively high concentrations of pesticides in drinking water. In the present study, we assessed the potential for occurrence of pesticides in drinking water of residents of 15 rural communities situated in the northern Great Plains in Canada (Figure 1).



Figure 1

Study area showing the locations of drinking water reservoirs in Manitoba, Saskatchewan, and Alberta, Canada.

Pesticides in Surface Drinking-Water Supplies of the Northern Great Plains

Ingestion in food is a major pathway of cadmium (Cd) exposure for humans It is therefore desirable to ensure that Cd concentrations in crops that enter the human food chain do not increase to levels that may lead to health risks Phosphorus fertilizers contain Cd as a contaminant at levels varying from trace amounts to as much as 300 mg Cd kg–1 of dry product and therefore can be a major source of Cd input to agricultural systems Fertilization can influence Cd accumulation in crops by direct Cd addition and by indirect effects on soil pH, ionic strength, Zn concentration, rhizosphere chemistry, microbial activity, and plant growth Cadmium will accumulate in the soils from fertilizer applications if the amount of Cd added in fertilizer is greater than the amount of Cd removal, whether in harvested crop removal or other loss pathways such as leaching, erosion, or bioturbation Assessment of the impact of fertilizer management practices on the risk of Cd toxicity to the soil ecosystem and the ris

Fertilizer Impacts on Cadmium Availability in Agricultural Soils and Crops

Adsorption of dicamba (3,6-dichloro-2-methoxy benzoic acid) in aqueous solution by calcined–layered double hydroxide

The degradation of 4-chloro-2-methylphenol (PCOC) in aqueous solution by UV irradiation in the presence of TiO2 has been studied. It was found that only 51.4% of PCOC was degraded by this process. The improvement in degradation levels were achieved by using various oxidants as electron scavenger. Periodate ion was found to be much more efficient oxidant than the others in improving the degradation of PCOC via formation of reactive species. The effect of the oxidants used in the UV/TiO2 systems on the degradation rate of PCOC were found to be in the order of IO4− > BrO3− > H2O2 > O2> ClO3−. Addition of metal ions to UV/TiO2/H2O2 system increased the photodegradation rate of the organic substrate. The effect of Mn2+, Cr3+, Fe2+ and Fe3+ metal ions on degradation of PCOC in the TiO2/UV/H2O2/Mn+ system was found to be in the order of Fe3+ > Fe2+ > Mn2+ > Cr3+. Langmuir–Hinshelwood rate expression was employed for the degradation of PCOC by the UV/TiO2/O2 system and adsorption equilibrium constant and the rate constant were determined to be 74.16 mM−1 and 0.0081 mM min−1, respectively.

Degradation of 4-chloro-2-methylphenol in aqueous solution by UV irradiation in the presence of titanium dioxide

Protocols for Deriving Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses

Literature on the environmental fate and effects of the benzoic acid herbicide dicamba was reviewed to provide a scientific basis to derive Canadian Water Quality Guidelines. Included in the review was information on the uses and production of dicamba, its physical and chemical properties, environmental monitoring data in Canadian surface water and groundwater, soils, sediments, and biota, and its environmental degradation, persistence, and fate. Through monitoring, dicamba has been detected in less than 8% of surface-water samples to a maximum concentration of 13 micrograms.L-1, while 2% of groundwater samples were positive up to 517 micrograms.L-1. Only one study that analyzed sediments (with no detections) and no field studies that investigated residues in biota were found. Microbial degradation is the most important process governing the dissipation of dicamba in aquatic and soil environments. Photolysis, hydrolysis, volatilization, adsorption to sediment, and bioconcentration are not expected to be significant removal processes, based on limited environmental fate data. The half-life of dicamba in water is 100 mg.L-1. No chronic data were found for either of these groups. The chronic EC50 to 14 freshwater algae, based on growth inhibition, ranged from 100 to > 10,000 micrograms.L-1. No studies on freshwater macrophytes or any marine organisms were found. Agricultural crops exhibited varying toxicity.(ABSTRACT TRUNCATED AT 400 WORDS)

Environmental fate and effects of dicamba: a Canadian perspective

A review of the environmental chemistry, fate, and toxicology of the herbicide MCPA was conducted. MCPA is used worldwide and is among the top ten herbicides sold in Canada. It has a systemic effect and is used to control a large range of broadleaf weeds in agricultural and noncrop lands. MCPA is highly water soluble and has a low affinity for most soil types, which gives it the potential to leach and contaminate groundwaters. It can undergo microbial degradation in aerobic conditions; therefore, it is only slightly persistent in soil and water. In Canada, MCPA has been detected in surface waters at levels varying between 0.00003 and 0.013 mg/l, and at relatively high levels in some groundwater (1.0 mg/1). It has also been reported to affect organisms such as the diatom Navicula pelliculosa at levels as low as of 0.026 mg/1, and the beagle dog at concentrations of 0.75 mg/kg/d. This review includes the development of the Canadian Water Quality Guidelines for MCPA, which are numerical concentratio...

D. D. MacDonald

Papers

Protocols for Deriving Canadian Water Quality Guidelines for the Protection of Agricultural Water Uses

Environmental fate and effects of dicamba: a Canadian perspective

Environmental fate and effects of MCPA: A Canadian perspective