Groundwater salinity in the Horn of Africa: Spatial prediction modeling and estimated people at risk

BACKGROUND

Changes in climate and anthropogenic activities have made water salinization a significant threat worldwide, affecting biodiversity, crop productivity and contributing to water insecurity. The Horn of Africa, which includes eastern Ethiopia, northeast Kenya, Eritrea, Djibouti, and Somalia, has natural characteristics that favor high groundwater salinity. Excess salinity has been linked to infrastructure and health problems, including increased infant mortality. This region has suffered successive droughts that have limited the availability of safe drinking water resources, leading to a humanitarian crisis for which little spatially explicit information about groundwater salinity is available.

METHODS

Machine learning (random forest) is used to make spatial predictions of salinity levels at three electrical conductivity (EC) thresholds using data from 8646 boreholes and wells along with environmental predictor variables. Attention is paid to understanding the input data, balancing classes, performing many iterations, specifying cut-off values, employing spatial cross-validation, and identifying spatial uncertainties.

RESULTS

Estimates are made for this transboundary region of the population potentially exposed to hazardous salinity levels. The findings indicate that about 11.6 million people (∼7% of the total population), including 400,000 infants and half a million pregnant women, rely on groundwater for drinking and live in areas of high groundwater salinity (EC > 1500 µS/cm). Somalia is the most affected and has the largest number of people potentially exposed. Around 50% of the Somali population (5 million people) may be exposed to unsafe salinity levels in their drinking water. In only five of Somalia's 18 regions are less than 50% of infants potentially exposed to unsafe salinity levels. The main drivers of high salinity include precipitation, groundwater recharge, evaporation, ocean proximity, and fractured rocks. The combined overall accuracy and area under the curve of multiple runs is ∼ 82%.

CONCLUSIONS

The modelled groundwater salinity maps for three different salinity thresholds in the Horn of Africa highlight the uneven spatial distribution of salinity in the studied countries and the large area affected, which is mainly arid flat lowlands. The results of this study provide the first detailed mapping of groundwater salinity in the region, providing essential information for water and health scientists along with decision-makers to identify and prioritize areas and populations in need of assistance.

Geogenic manganese and iron in groundwater of Southeast Asia and Bangladesh - Machine learning spatial prediction modeling and comparison with arsenic

Naturally occurring, geogenic manganese (Mn) and iron (Fe) are frequently found dissolved in groundwater at concentrations that make the water difficult to use (deposits, unpleasant taste) or, in the case of Mn, a potential health hazard. Over 6000 groundwater measurements of Mn and Fe in Southeast Asia and Bangladesh were assembled and statistically examined with other physicochemical parameters. The machine learning methods random forest and generalized boosted regression modeling were used with spatially continuous environmental parameters (climate, geology, soil, topography) to model and map the probability of groundwater Mn > 400 μg/L and Fe > 0.3 mg/L for Southeast Asia and Bangladesh. The modeling indicated that drier climatic conditions are associated with a tendency of elevated Mn concentrations, whereas high Fe concentrations tend to be found in a more humid climate with elevated levels of soil organic carbon. The spatial distribution of Mn > 400 μg/L and Fe > 0.3 mg/L was compared and contrasted with that of the critical geogenic contaminant arsenic (As), confirming that high Fe concentrations are often associated with high As concentrations, whereas areas of high concentrations of Mn and As are frequently found adjacent to each other. The probability maps draw attention to areas prone to elevated concentrations of geogenic Mn and Fe in groundwater and can help direct efforts to mitigate their negative effects. The greatest Mn hazard is found in densely populated northwest Bangladesh and the Mekong, Red and Ma River Deltas of Cambodia and Vietnam. Widespread elevated Fe concentrations and their associated negative effects on water infrastructure pose challenges to water supply. The Mn and Fe prediction maps demonstrate the value of machine learning for the geospatial prediction modeling and mapping of groundwater contaminants as well as the potential for further constituents to be targeted by this novel approach.

Fluoride contamination of groundwater resources in Ghana: Country-wide hazard modeling and estimated population at risk

Most people in Ghana have no or only basic access to safely managed water. Especially in rural areas, much of the population relies on groundwater for drinking, which can be contaminated with fluoride and lead to dental fluorosis. Children under the age of two are particularly susceptible to the adverse effects of fluoride and can retain 80-90% of a fluoride dose, compared to 60% in adults. Despite numerous local studies, no spatially continuous picture exists of the fluoride contamination across Ghana, nor is there any estimate of what proportion of the population is potentially exposed to unsafe fluoride levels. Here, we spatially model the probability of fluoride concentrations exceeding 1.0 mg/L in groundwater across Ghana to identify risk areas and estimate the number of children and adults exposed to unsafe fluoride levels in drinking water. We use a set of geospatial predictor variables with random forest modeling and evaluate the model performance through spatial cross-validation. We found that approximately 15% of the area of Ghana, mainly in the northeast, has a high probability of fluoride contamination. The total at-risk population is about 920,000 persons, or 3% of the population, with an estimated 240,000 children (0-9 years) in at-risk areas. In some districts, such as Karaga, Gushiegu, Tamale and Mion, 4 out of 10 children are potentially exposed to fluoride poisoning. Geology and high evapotranspiration are the main drivers of fluoride enrichment in groundwater. Consequently, climate change might put even greater pressure on the area's water resources. Our hazard maps should raise awareness and understanding of geogenic fluoride contamination in Ghana and can advise decision making at local levels to avoid or mitigate fluoride-related risks.

Residue depletion of oxytetracycline (OTC) and 4-epi-oxytetracycline (4-epi-OTC) in broiler chicken's claws by liquid chromatography-tandem mass spectrometry (LC-MS/MS)

Antibiotics are widely used in poultry production for the treatment of bacterial diseases. However, residues may remain in products and by-products destined for human consumption or animal feeding. The claws of chickens, which are a by-product of the poultry industry, can directly or indirectly enter the food chain as meals destined to feed other productive animals. Thus, it becomes necessary to determine and quantify antimicrobial residues present in this matrix. The objective of the study was to assess the depletion of oxytetracycline (OTC) and its metabolite 4-epi-OTC in broiler chicken's claws. Claws of 32 broilers treated with a therapeutic dosage of 10% OTC during 7 days were analysed. Samples were taken at days 3, 9, 15 and 19 post-treatment. As for the control group, eight broiler chickens were raised under the same conditions. Extraction was carried out through EDTA-McIlvaine buffer, and clean-up employed a SPE C-18 Sep-Pak®. Instrumental analysis was performed through LC-MS/MS. The concentrations of both analytes were determined in claw samples until day 19 post-treatment. Average concentrations were within the LOD (20 μg kg^-1) and LOQ (22 µg kg^-1) for OTC and 84 μg kg^-1 for 4-epi-OTC. Withdrawal times (WDTs) of 39 days for OTC and 54 days for 4-epi-OTC were established in claws based on 95% confidence. These findings demonstrate that claws can be a source of antimicrobial residue entry into the food chain, since the results showed that OTC and its metabolite can be found in chicken's claws for long periods, even exceeding the average lifespan of a broiler chicken.

Ovine Echinococcus granulosus transmission dynamics in the province of Rio Negro, Argentina, 1980-1999

In this work, the impact of a hydatidosis control programme for dogs on the intermediate ovine host was specifically analysed to determine the levels of prevalence achieved and the dynamics of parasite transmission, as well as to evaluate the quality of diagnostic systems in slaughterhouses. A field study was conducted in four slaughterhouses (Valcheta, Los Menucos, Jacobacci, Bariloche) that process animals coming from all the departments within the work area. The control programme for dogs entailed treating dogs with 5 mg/kg praziquantel at 2-month intervals for 20 years. Sample size was determined with a 10% error margin and a 95% significance level. Harvested viscera (liver, lungs, kidneys) were preserved in 5% formaldehyde and sent to the laboratory for diagnostic confirmation of both positive and negative specimens. The 61% initial prevalence dropped to 18.3% at the end of the 10-year period, observed differences proving significant (Chi-square=15.454, P=0.00). There were statistically significant increases in infection prevalence with age (Pearson's Chi-square=133.61, P=0.00). Overall, 37.2% of hydatidosis cases diagnosed in slaughterhouses were considered non-hydatid by histological study. On the other hand, 1.1% of those diagnosed as healthy were found to be infected with hydatidosis. The number of hydatid cysts per animal increased with age: 0.04 in lambs and 1.22 in adults (linear regression equation, -0.0539+0.0127 x age), whereas the average for the whole period was 3.7% in lambs and 20.5% in adults. Viability studies indicated that 63.8% of parasitised animals had viable cysts, out of which 53.3% were fertile. Diagnosis of infection in sheep made by means of an adjusted statistical design and with histological confirmation of the presumptive diagnosis made in slaughterhouses demonstrated the flaws of the official systems for epidemic surveillance of hydatidosis. However, there was no overall significant difference in slaughterhouse and laboratory data.Ro was 0.53 and could imply a decrease in reproductive capacity of the parasite and steady state extinction.

Rate of infection and of reinfection by Echinococcus granulosus in rural dogs of the province of Rio Negro, Argentina

Hydatidosis (cystic echinococcosis) constitutes a serious public health problem in the Province of Rio Negro, Argentina. In the present work it was intended to evaluate the prevalence of the canine echinococcosis in rural areas of the Province of Rio Negro and studied the reinfection rate in dogs after treatment with Praziquantel during the period 1980-1997. A total of 496 dogs were studied in 18 canine concentrations in order to establish the initial prevalence rate which was 42.3%. From 1980 onward dogs should have been systematically treated with anthelmintic every 2 months in rural areas and every 6 months in urban areas. We estimated that approximately 65% of dogs were treated. To determine the reinfection rate, 476 dogs (1984) and 598 dogs (1996) were studied after anthelmintic treatment during two sequential time periods (0-45; 46-90 days). In both cases treated animals were compared with untreated dogs. Prevalences were 3.5%, 6.7% and 21.3% in 1984 and 0.8%, 4.0% and 10.0% in 1996. For the purpose of surveillance a total number of 21,444 dogs were studied during 18 years. Prevalence of Echinococcus granulosus decreased significantly in the first year from 42.3% to 6.1%.

Repeated tuberculin testing in patients with active pulmonary tuberculosis

OBJECTIVE

The proportion of tuberculin reactors in a population and the intensity of tuberculin reactions have been shown to increase with increasing exposure to mycobacterial infection, eg, repeated BCG immunization. These observations suggested that tuberculin reactivity would become uniformly high in individuals with a high mycobacterial load who did not have a known cause of anergy. Since tuberculin reactivity has been measured to evaluate the possible genetic regulation of responses to mycobacteria in humans, it is important to study its behavior under conditions of ongoing, maximal exposure to mycobacteria. In the present study, we determined the mean size of tuberculin reactivity in BCG-immunized and unimmunized patients with pulmonary tuberculosis of recent onset, and the stability of tuberculin reactions during and after treatment of pulmonary tuberculosis.

METHOD

Serial tuberculin testing was performed on patients with newly diagnosed active pulmonary tuberculosis diagnosed over a period of 2 years at the National Institute for Respiratory Diseases in Santiago, Chile. The first tuberculin test was performed at the time of diagnosis in 58 patients. Repeated tuberculin testing was performed 2 weeks later in 15 patients with initial reaction sizes < 15 mm. Four additional tuberculin tests were performed, one each at 3-months intervals in 42 patients regardless of the size of the initial tuberculin reaction.

RESULTS

Tuberculin reactions at entry had a unimodal distribution in patients both with and without BCG scars (14.8 +/- 5.0 mm and 16.5 +/- 5.2 mm, respectively). A second tuberculin test in patients with initial reaction sizes < 15 mm showed a moderate, statistically significant increase in the mean reaction size (PPD1: 10.1 +/- 3.2 mm; PPD2: 11.9 +/- 4.8 mm). Repeated tuberculin testing over 1 year revealed no significant changes in reaction size. The mean reaction sizes were 15.8 +/- 5.0 mm at entry, 15.5 +/- 5.4 mm at 3 months, 17.2 +/- 5.2 mm at 6 months, 17.0 +/- 5.1 mm at 9 months, and 16.7 +/- 54 mm at 12 months. The standard deviation of a random observation within patients was 5.3 mm. The largest variations due to increased reactivity after 6 months of treatment were observed in patients with reaction < 15 mm at entry compared with hyperergic patients, and in BCG-immunized patients compared to unimmunized patients.

CONCLUSIONS

In the presence of an ongoing mycobacterial infection, patients without anergizing conditions express a tuberculin reactivity that is relatively constant during and after treatment of pulmonary tuberculosis. The size and stability of the reactions seem to be determined by individual conditions that include the tuberculin reactivity at the time of diagnosis and the BCG immunization status.