Efficiencies of available organic mixtures for the biological treatment of highly acidic-sulphate rich drainage of the San Jose mine, Bolivia.

The environmental contamination due to mining activities in the Andean region of Bolivia is a serious concern, as it leads to highly acidic (pH 2.4) acid mine drainage (AMD), severely polluted by sulfate (>12,000 mg L-1). Passive bioreactors entailing biological sulfate reduction and removal of metals through sulfide precipitation have been recognized as a promising biotechnology. The reactivity of mixtures containing locally available substrates: sheep manure, compost and straw, was assessed through batch experiments conducted with a synthetic solution simulating the composition of AMD from San José mine (Oruro). The removal of sulfate and metals was successful in all reactors, at the end of the experiment (56 days) sulfate concentrations dropped to 1378-2081 mg L-1, corresponding to a removal efficiency between 84% and 89%, while average removal for Fe, Zn, Pb, and Cd were 99.8%, 98.5%, 94.7%, 98.6%, respectively. The sulfate and metal removal showed three phases. In the first phase, the removal was independent of the organic composition and attributable to pH-controlled mechanisms i.e. adsorption, precipitation of oxy(hydroxides) and co-precipitation. During the second phase, sulfate and metals concentrations remained rather constant; while in the third phase, the removal was affected by the organic matter composition. Sulfate removal rate attained the highest values (227-243 mg L-1 d-1) in the third phase, and it was attributable to biological reduction with not sulfate limitation. The depletion of nutrients rather than the sulfate availability may have limited the sulfate removal at the end of the experiment.

Evaluación del daño renal por cadmio en población expuesta a contaminación por éste en agricultores de Quila-Quila, Potosí / Evaluation of kidney damage by cadmium in a population exposed to its contamination in farmers from Quila-Quila, Potosí

El cadmio es un metal pesado presente en desechos mineros y otros, y tiene efectos deletéreos en la salud humana especialmente en el riñón en el que destruye células tubulares. En una investigación de la calidad del lecho de los ríos que reciben aguas residuales en el norte de Potosí, Bolivia, se reportó presencia de cadmio en papas regadas con esa agua en Quila-quila, una población rural de la zona. OBJETIVO: de este trabajo fue el de identificar posibles daños del cadmio en la salud de los pobladores de Quila-quila. MÉTODOS: para ello se realizó revisión clínica y análisis laboratorial clínico y químico de sangre y orina de los pobladores de Quila-quila, y se calculó la tasa de filtración glomerular (TFG) y se correlacionó ésta con indicadores de lesión glomerular. RESULTADOS: se encontraron niveles elevados de cadmio en sangre en algunas personas, y una correlación de la TFG con la concentración de cadmio en sangre y con indicadores de lesión de membrana glomerular. CONCLUSIONES: en conclusión, los pobladores de Quila-quila estuvieron contaminados por cadmio, el cual produjo lesión renal leve.

Cadmium is a heavy metal present in mining and other wastes, and has deleterious effects on human health especially in the kidney in which it destroys tubular cells. In an investigation of the quality of the river beds that receive wastewater in the north of Potosí, Bolivia, the presence of cadmium was reported in potatoes watered with these water in Quila-quila, a rural town in the area. OBJECTIVE: of this work was to identify possible damage from cadmium to the health of the inhabitants of Quila-quila. METHODS: for this, clinical review and clinical and chemical laboratory analysis of blood and urine from the inhabitants of Quila-quila, and the filtration rate was calculated glomerular (GFR) and this was correlated with indicators of glomerular injury. RESULTS: elevated levels of cadmium were found in the blood in some people, and a correlation of GFR with blood cadmium concentration and indicators of membrane injury glomerular. CONCLUSIONS: in conclusion, the inhabitants of Quila-quila were contaminated by cadmium, which caused mild kidney damage.

Pathogens in crop production systems irrigated with low-quality water in Bolivia.

In dry areas, the need for irrigation to ensure agricultural production determines the use of all available water sources. However, the water sources used for irrigation are often contaminated by untreated or minimally treated wastewater. Microbial risks from reusing wastewater for vegetable irrigation can be addressed by installing environmental barriers that pathogens must cross to reach humans in the reuse system. Knowledge of pathogen flows inside the system and pathogen removal potential is the first step towards devising a risk management strategy. This study assessed microbe prevalence in farming systems in the Bolivian highlands that use wastewater-polluted sources for irrigation of lettuce. Samples of soil, lettuce and different water sources used in the farming systems were taken during one crop season and concentrations of coliphages, Escherichia coli and helminth eggs were measured. The results showed high spread of these microorganisms throughout the whole system. There was a significant correlation between microbial quality of water and of the harvested produce for several microorganisms. The microbial prevalence in protected shallow wells was found to be significantly lower than in other water sources. These findings can help formulate feasible risk management strategies in contexts where conventional technologies for microbial removal are not possible.

Identifying the cause of soil cadmium contamination with Monte Carlo mass balance modelling: a case study from Potosi, Bolivia.

The Chayanta river in Potosi, Bolivia is polluted by present and past mining activities in the districts of Siglo XX and Llallagua. The river water, which is enriched with cadmium (Cd), is used for irrigation in the Quila Quila and Asiruri valleys where the median soil Cd concentration is 20 mg kg(-1), well above the background value of < 0.5 mg kg(-1). The objective of this study was to predict current soil contamination using a retrospective mass balance. Monitoring data were collected on Cd concentrations in irrigation water, irrigation application rates, crop yield and composition, and soil properties including pore water composition. The mass balance was made assuming constant model parameters since the start of upstream mining operations about 85 years ago (1920). The parameter uncertainty was taken into account with a Monte Carlo analysis. The current annual Cd input by irrigation is 800 g ha(-1). The annual output of Cd through removal of the crop harvest and leaching is less than 10 g ha(-1). The predicted soil Cd concentrations after 85 years of contamination (geometric mean: 21.9 mg x kg(-1), 10th and 90th percentile 7.2-65.1 mg kg(-1) respectively) matched the distribution of observed values (geometric mean: 18.6 mg kg(-1); 10th and 90th percentile 4.7-65.9 mg kg(-1) respectively; n = 56). This study confirmed that irrigation water is the prime source of soil Cd enrichment in that area. The Monte Carlo analysis is a convenient way of including parameter uncertainty in mass balance modelling and of estimating spatial variability of the contamination.

Elevated cadmium concentrations in potato tubers due to irrigation with river water contaminated by mining in Potosí, Bolivia.

Risk of cadmium (Cd) in the human food chain in Cd-contaminated areas is often limited by phytotoxicity from zinc (Zn) that is associated with the Cd contamination. A semiarid area, 60 km downstream of a tin mine in Bolivia, was surveyed where irrigation with Cd-contaminated river water (65-240 microg Cd L(-1)) has increased median soil Cd to 20 mg kg(-1) while median soil Zn was only about 260 mg kg(-1). Cadmium concentrations in potato tubers increased from background values (0.05 mg kg(-1) dry wt.) in soils irrigated with spring water to a median value of 1.2 mg kg(-1) dry wt. in the affected area. Median concentration of Cd in soil solutions was 27 microg L(-1) and exceeded the corresponding value of Zn almost twofold. Soil-extractable chloride ranged from 40 to 1600 mg Cl(-) kg(-1) and was positively correlated with soil total Cd. Increasing soil solution Cl(-) decreased the solid-liquid distribution coefficient of Cd in soil. Soil total Cd explained 64% of the variation of tuber Cd concentration while only 3% of the variation was explained by soil extractable Cl(-) (n = 49). The estimated dietary Cd intake from potato consumption by the local population is about 100 microg d(-1) which exceeds the WHO recommended total daily intake. It is concluded that the food chain risk of Cd in the irrigation water of the semiarid area is aggravated by the association with Cl(-) and, potentially, by the relatively large Cd/Zn ratio.

Experimental study and modelling of Cr (VI) removal from wastewater using Lemna minor.

The removal of Cr(VI) from wastewater by Lemna minor was studied both at laboratory and pilot scale. Laboratory tests were conducted under different conditions of initial Cr(VI) concentration (0.5 and 2.0 mg/l) and temperature (285 and 291 K). Batch experiments were carried out during 16 days in which the chromium concentrations, both in the biomass and in wastewater were measured. Data were used to characterize the biouptake capacity of the biomass; results showed that it increases with the temperature and when the initial Cr concentration decreases. The biouptake process could be fitted by an equation, with a correlation coefficient of 0.98. The removal process was assessed using the data of the variation of chromium concentration in the wastewater with respect to time; this allowed obtaining constant parameters which were applied in a mathematical model for the assessment of duckweed systems in a pilot scale plant.