Contaminaci.n por ars.nico en aguas subterr.neas en la provincia de Valladolid: variaciones estacionales.

English. In 2000, high concentration levels of Arsenic were detected in several ground water sources located in the province of Valladolid (Spain). Further investigations delimited an area of approximately 1700 square km with a geographical centre at the city of Iscar. In this area, ground water is usually used for agricultural purposes. However, ground water was also used as drinking water, the observed arsenic concentrations being frequently above of the allowable limit. The objectives of this work were: a) to estimate the concentration levels of As in the zone, in order to determine the actual magnitude of the problem and also to select a group of points as a monitoring network. b).- To perform the monitoring through the sampling network. A initial survey was carried out in 63 sampling points. The average value of Arsenic concentration was 38 micro g/L (ranging from <1 to 177 micro g/L). Aproximately, the 88% of the sampling points were above of the allowable limit for drinking waters established at 10 micro g/L by the World Health Organization. The 32% of the sampling points were above of 50 micro g/L. Aprox. 10% of the sampling points showed concentrations above of 100 micro g/L. Taking into account these preliminary results, 14 points were selected as a monitoring network. Sampling was carried from June-2002 to July-2003 and no significant differences were found in observed concentrations in different months, in spite of the significant different water levels in wells. In this work, the monitoring work is presented and the incidence of several physic-chemical parameters as pH, redox potential, conductivity Fe and P content in observed As concentrations is discussed.

Spanish; Castilian. En el a.o 2000 se detectan los primeros pozos con elevados niveles de As en la zona de .scar (Valladolid). Estudios posteriores delimitan un .rea afectada de unos 1700 km cuadrados, de forma triangular, con centro geogr.fico en Iscar. El agua de estos pozos se utiliza sobre todo para el riego de los cultivos de la zona pero en algunos casos tambi.n se emplea como agua de consumo. Los niveles de As encontrados resultan, en muchos casos, superiores a la concentraci.n m.xima admisible en aguas potables, seg.n la Organizaci.n Mundial de la Salud. Los objetivos de este trabajo son: a.- Determinaci.n del nivel de As en diferentes puntos de la zona afectada, con el fin de establecer la extensi.n del problema y seleccionar una serie de pozos (red de control) para el estudio de su evoluci.n temporal, b.- Seguimiento de la evoluci.n de la concentraci.n de As en los pozos de la red de control a lo El muestreo inicial se llev. a cabo en 63 puntos situados en la zona afectada. El valor medio hallado fue de 38 micro g de As/L (con valores m.ximos pr.ximos a 200 micro g/L). El 88 % de los pozos superaron la concentraci.n de 10 micro g/L y el 32 % superaron 50 micro g/L. Casi un 10 % super. 100 micro g/L. A partir de estos datos se seleccionaron 14 puntos de control, de los que se tomaron muestras mensualmente, desde junio de 2002 hasta julio de 2003. Durante el .ltimo a.o, no se detectaron diferencias significativas en la concentraci.n en los diferentes meses, a pesar de que el nivel de agua en los pozos s. ha sufrido variaciones significativas. Se discute la relaci.n entre la concentraci.n de As y otros par.metros f.sico-qu.micos, como son pH, potencial redox, hierro y f.sforo.