Ruth M. Loewy

Pesticide distribution in an agricultural environment in Argentina

An assessment of the off-site migration of pesticides from agricultural activity into the environment in the Neuquen River Valley was performed. The aim of this study was to evaluate the distribution of pesticides in several compartments of a small agricultural sub-catchment. Soil, surface water, shallow groundwater and drift deposition were analyzed for pesticide residues. Results showed the presence of some pesticide residues in soil, surface water and shallow groundwater compartments. The highest detection frequencies in water (surface and subsurface) were found for azinphos-methyl and chlorpyrifos (>70%). In terms of concentration, the highest levels were observed in shallow groundwater for azinphos methyl (22.5 μg/L) and carbaryl (45.7 μg/L). In the soil, even before the application period had started, accumulation of residues was present. These residues increased during the period studied. Spray drift during pesticide application was found to be a significant pathway for the migration of pesticide residues in surface water, while leaching and preferential flows were the main transport routes contributing to subsurface contamination.

Effect of pesticide use in fruit production orchards on shallow ground water.

As a part of landscape‐scale study, ground water samples were collected from 30 wells located in fruit production farms belonging to the valley of Neuquen river during the period 1995–1998 and analyzed for organophosphate pesticides. As a consequence of the leaching process, ground water from the Valley of Neuquen River frequently contained concentrations of organophosphorus pesticides that exceeded acute toxicity risk ratios established to protect aquatic life. It was found that some pesticides, as azinphos methyl, had a high detection frequency, 66% of the samples, with concentrations varying from no detection to 48.9 ppb. Dimethoate, metidathion and phosmet were also detected with frequencies of 14.1, 13.6 and 10.8% and with concentration ranks from no detection to a maximum value of 10.9, 2.0 and 15.5 ppb, respectively. Seasonal variations and temporal trends were found for these compounds in ground water.

Azinphos Methyl Residues in Shallow Groundwater from the Fruit Production Region of Northern Patagonia, Argentina

Groundwater samples were collected from monitoring wells along an area of intensive fruit production. Different types of correlations were investigated between soil physicochemical characteristics, depths and agricultural practices with pesticide detection frequency. In the three analyzed periods azinphos methyl, S-(3,4-diydro-4-oxobenzo[d]-[1,2,3]-triazin-3-ylmethyl)-O,O-dimethyl phosphorodithioate, showed a definite seasonal behavior related to the application pattern, increasing its concentration in the aquifer from October to November-December and then decreasing towards March. Samples obtained during the non-spraying season showed that azinphos methyl residues were lower than detection limit (LOD). An inverse correlation was observed between azinphos methyl concentration and the time elapsed since the last pesticide application. Seasonal events such as rain and irrigation influence the chemical concentration in the well, while no correlation was obtained between soil characteristics and azinphos methyl concentration. The soil attenuation capacity was not enough to prevent the presence of azinphos methyl in the aquifer during the application season.

Sources and distribution of aliphatic and polyaromatic hydrocarbons in sediments from the Neuquen River, Argentine Patagonia

Spatial distribution and probable sources of aliphatic and polyaromatic hydrocarbons (AHs, PAHs) were investigated in surface sediments collected along the bank of the Neuquen River, Argentina. Total concentrations of aliphatic hydrocarbons ranged between 0.41 and 125 μg/g dw. Six stations presented low values of resolved aliphatic hydrocarbons and the n–alkane distribution indexes applied suggested a clear biogenic source. These values can be considered the baseline levels of aliphatic hydrocarbons for the river sediments. This constitutes important information for the assessment of future impacts since a strong impulse in the exploitation of shale gas and shale oil in these zones is nowadays undergoing. For the other 11 stations, a mixture of aliphatic hydrocarbons of petrogenic and biogenic origin was observed. The spatial distribution reflects local inputs of these pollutants with a significant increase in concentrations in the lower course, where two major cities are located. The highest values of total aliphatic hydrocarbons were found in this sector which, in turn, was the only one where individual PAHs were detected.

The impact of pesticides on the macroinvertebrate community in the water channels of the Río Negro and Neuquén Valley, North Patagonia (Argentina)

Agriculture represents the second most important economic activity in the North Patagonian Region of Argentina and non-selective insecticides are still being used with significant implications to the quality of the environment. The range of concentrations (μg/L) determined for azinphosmethyl, chlorpyrifos, and carbaryl in drainage channels were from non-detected to 1.02, 1.45, and 11.21, respectively. Macroinvertebrate abundance and taxon richness in drainage channels were significantly lower in November compared to the other sampling months (October, February). The decrease in taxon richness observed in November was associated with chlorpyrifos and azinphosmethyl peak concentrations. The most remarkable changes were the decrease in sensitive taxa such as Baetidae and the increase in some tolerant taxa such as Chironomidae and Gastropoda.For all three pesticides, the acute hazard quotient exceeded the risk criteria for invertebrates. The effects of the three pesticides on aquatic organisms, characterized by joint probability curves, showed that the LC50 of 10% of the species were exceeded five and three times by the concentrations of azinphosmethyl and chlorpyrifos during the study period, respectively. However, the correlation between the pesticide concentrations and both taxon richness and abundance of macroinvertebrates at each site (irrigation and drainage channels) was indicative that only chlorpyrifos was negatively correlated with both parameters (Spearman r2 − 0.61, p = 0.0051 and Spearman r2 − 0.59, p = 0.0068 for taxon richness and abundance correlation, respectively). We conclude that macroinvertebrate assemblages in drainage channels were highly affected by chlorpyrifos levels.