The effect of non-fluoride factors on risk of dental fluorosis: evidence from rural populations of the Main Ethiopian Rift.

Elevated level of fluoride (F(-)) in drinking water is a well-recognized risk factor of dental fluorosis (DF). While considering optimization of region-specific standards for F(-), it is reasonable, however, to consider how local diet, water sourcing practices, and non-F(-) elements in water may be related to health outcomes. In this study, we hypothesized that non-F(-) elements in groundwater and lifestyle and demographic characteristics may be independent predictors or modifiers of the effects of F(-) on teeth. Dental examinations were conducted among 1094 inhabitants from 399 randomly-selected households of 20 rural communities of the Ziway-Shala lake basin of the Main Ethiopian Rift. DF severity was evaluated using the Thylstrup-Fejerskov Index (TFI). Household surveys were performed and water samples were collected from community water sources. To consider interrelations between the teeth within individual (in terms of DF severity) and between F(-) and non-F(-) elements in groundwater, the statistical methods of regression analysis, mixed models, and principal component analysis were used. About 90% of study participants consumed water from wells with F(-) levels above the WHO recommended standard of 1.5mg/l. More than 62% of the study population had DF. F(-) levels were a major factor associated with DF. Age, sex, and milk consumption (both cow's and breastfed) were also statistically significantly (p<0.05) associated with DF severity; these associations appear both independently and as modifiers of those identified between F(-) concentration and DF severity. Among 35 examined elements in groundwater, Ca, Al, Cu, and Rb were found to be significantly correlated with dental health outcomes among the residents exposed to water with excessive F(-) concentrations. Quantitative estimates obtained in our study can be used to explore new water treatment strategies, water safety and quality regulations, and lifestyle recommendations which may be more appropriate for this highly populated region.

Arsenic exposure of rural populations from the Rift Valley of Ethiopia as monitored by keratin in toenails.

Arsenic (As) contamination of drinking water is a worldwide phenomenon whose effect among vulnerable and rural communities in the Rift Valley of Ethiopia in eastern Africa is not well studied. This study examines As exposure and bioaccumulation from drinking water by monitoring human keratin in the form of toenails from exposed populations. Groundwater samples from drinking water wells (n=34) were collected along with toenail samples (n=58) from local communities and were analyzed for trace metals including As by inductively coupled plasma mass spectrometry (ICP-MS). Of the total number of wells tested, 53% had As level above the WHO maximum contamination level of 10 p.p.b. Arsenic in toenails was significantly correlated to corresponding drinking water (r=0.72; R(2)=0.52; P<0.001). This correlation improves for drinking water with As concentrations above 2 p.p.b. (r=0.74; R(2)=0.54; P<0.001). Male minors (<18 years old) were found to have greater nail-As concentrations compared with adults consuming equal amounts of As (P<0.05). Estimated As dose specifically from drinking water sources was also associated with nail concentrations (P<0.01). We suggest that As measurement in nails could be a reliable method for detecting As exposure in residents living in rural areas.

Cumulative impacts of mountaintop mining on an Appalachian watershed.

Mountaintop mining is the dominant form of coal mining and the largest driver of land cover change in the central Appalachians. The waste rock from these surface mines is disposed of in the adjacent river valleys, leading to a burial of headwater streams and dramatic increases in salinity and trace metal concentrations immediately downstream. In this synoptic study we document the cumulative impact of more than 100 mining discharge outlets and approximately 28 km(2) of active and reclaimed surface coal mines on the Upper Mud River of West Virginia. We measured the concentrations of major and trace elements within the tributaries and the mainstem and found that upstream of the mines water quality was equivalent to state reference sites. However, as eight separate mining-impacted tributaries contributed their flow, conductivity and the concentrations of selenium, sulfate, magnesium, and other inorganic solutes increased at a rate directly proportional to the upstream areal extent of mining. We found strong linear correlations between the concentrations of these contaminants in the river and the proportion of the contributing watershed in surface mines. All tributaries draining mountaintop-mining-impacted catchments were characterized by high conductivity and increased sulfate concentration, while concentrations of some solutes such as Se, Sr, and N were lower in the two tributaries draining reclaimed mines. Our results demonstrate the cumulative impact of multiple mines within a single catchment and provide evidence that mines reclaimed nearly two decades ago continue to contribute significantly to water quality degradation within this watershed.