THE IMPACT OF AGRICULTURAL ACTIVITY ON THE GEOCHEMISTRY OF URBAN DUST FROM ARID ENVIRONMENTS IN NORTHWESTERN MEXICO

Agricultural activity in arid and semi-arid environments is particularly fragile. Principally, water supply can be a problem faced because of low annual rainfall. Groundwater overuse and abuse in decades, and the consequent saltwater-intrusion into the la Costa aquifer, in Northwestern Mexico, led to the abandonment of some fields from La Costa agricultural fields, located around 50 km southwest of Hermosillo city, within the Sonoran Desert Province. La Costa has been among the most productive fields in Mexico. Additionally, smaller agricultural fields are located few kilometers north, northeast, and southwest of the city. During the Green Revolution in the 1970s, banned pesticides such as DDT were extensively used, producing a current environmental passive in agricultural soils worldwide. A recent study shows the presence of DDT among other pesticides in agricultural soils from La Costa fields, and highlights that historic and current use of organochlorine pesticides might represent a threat to human health and wildlife. On the other hand, Hermosillo is a city where anthropogenic activity contributes with contaminants into its own urban environment; therefore, different geochemical sources might be recorded on the urban dust (i.e. industrial, construction, mining, vehicular traffic, etc.). Preliminary concentrations of DDT among others pesticides are reported in the urban dust from Hermosillo. According to the concentrations of DDT and its metabolites, the application of this pesticide was done in the past. The combination of incorrect historic use of groundwater that caused the saltwater-intrusion and use of pesticides in La Costa agricultural fields, along with subsequent and partial abandonment of the fields, combined with factors from arid environments (e.g. high temperatures, low precipitation, poor vegetation cover, wind speed) may promote the incorporation of polluted dust into the prevailing NE winds, which eventually will reach the urban and rural zones in Sonora, and eventually, the southern U.S. border. The re-suspension and wind transport of polluted dust by past agricultural activity represent a passive contaminant, and considering the extensive areas of the fields, a potential health risk should be considered in arid zones of Northwestern Mexico.