Trace elements in natural water : the impact on quality, food preparation and production

The levels of arsenic (total and species) and other trace elements in natural waters of Argentina were analysed using inductively coupled plasma mass spectrometer (ICP-MS). In addition, a method was developed for the determination of Mo in waters using graphite furnace atomic absorption spectrometry (GFAAS) with an added palladium chemical modifier. The analysis of Mo in certified reference materials and water samples using both methods confirmed no statistical difference using a paired t-test (tcal = 0.276; tcrit = 2.160, df: 14 at p south-east La Pampa (17.66-319.39 μg/l) > southern Buenos Aires (39.6-189.4 μg/l) > Rio Negro/Rio Colorado (1.03-38.66 μg/l). The distribution of As species (using a field-based solid phase extraction method) were significantly different between the sampling regions. In most of the study areas the groundwater exceeded 10 μg/l AsT (World Health Organisation guideline for drinking water) and can be deemed to be not fit for human consumption since the calculated hazard quotient (HQ) >1. Apart from As, Mo and V also showed higher levels in groundwaters relating to the historical deposition of volcanic ash within the Chaco-Pampean plain of Argentina. The groundwaters from La Pampa ranged from 10 to 84 μg/l Mo. Surprisingly, one farm well south of Eduardo Castex (central-northern La Pampa) used for cattle drinking water had 1381.66 μg/l Mo. Significant positive correlations were found for As, Mo and V between groundwaters used on agricultural lands and the associated soils and pastures.The arsenic concentrations in groundwaters were found to be statistically correlated (r > 0.5) with the corresponding soils (total and exchangeable fraction) and plants (leaves and roots) at p < 0.01. Based on a sequential extraction method for soils, the uptake of arsenic from the soil exchangeable fraction by plants was found to be statistically correlated (rleaves = 0.5 and rroots = 0.7 at p < 0.01). Furthermore, the use of local groundwaters for food preparation (washing and cooking) alters the elemental composition of local foodstuffs (carrots, potatoes, onions and rice). The transfer of As, Mo, V, Mn, Fe, Cu, Zn from the water to foodstuffs was found to be dependent on the levels in the water, washing steps and the cooking process (time and method). A higher uptake of As, Mo and V by foodstuffs was observed when cooking with highly ‗contaminated‘ groundwaters, especially for rice. This may significantly increase the daily dietary intake of these elements as a function of food consumption. However, drinking water (2 l/day) is still considered the main contributor to the total daily intake of As, Mo and V for the local residents who rely upon groundwater as their source for drinking and cooking due to the lower Argentine food consumption rate (38 - 196 g/day). Similar trends were observed in West Bengal, India involving rice production and preparation (washing and cooking). Elevated levels were observed for As, Mn and Fe for all sample types (plants, soils, raw and prepared rice) in relation to the use of local groundwaters. Consumption of cooked rice (500 - 750 g/day) was observed to be the major contributor to the total daily dietary intake of As, Mn and Fe (depending on the rice variety) in the Indian study area when the local groundwater (94 μg/l AsT) was used in the preparation of rice, especially for local grown rice varieties.