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.

Characterization of soil organic matter by FT-IR spectroscopy and its relationship with chlorpyrifos sorption.

Sorption of non-ionic organic compounds to soil is usually expressed as the carbon-normalized partition coefficient (KOC) assuming that the main factor that influences the amount sorbed is the organic carbon content (OC) of the soil. However, KOC can vary across a range of soils. The influence of certain soil characteristics on the chlorpyrifos KOC values variation for 12 representative soils of the Northpatagonian Argentinian region with different physicochemical properties was investigated for this study. The chlorpyrifos sorption coefficients normalized by the OC content were experimentally obtained using the batch equilibrium method; the KOC values ranged between 9000-20,000 L kg-1. The soil characteristics assessed were pH, clay content and spectral data indicative of soil organic matter (SOM) quality measured by FT-IR on the whole soil. The bands considered in the spectroscopic analyses were those corresponding to the aliphatic components, 2947-2858 cm-1 (band A) and the hydrophilic components, 1647-1633 cm-1 (band B). A significant relationship was found (R2 = 0.66) between chlorpyrifos sorption (KOC) and the variables pH and A/B height band ratio. The correlation between the values predicted by the derived model and the experimental data was significant (r = 0.89 p < 0.05). Thus, this methodology could be used to estimate chlorpyrifos sorption coefficient through the use of a simple, rapid, and environmentally-friendly measurement. KOC analysis in relation to soil properties represents a valuable contribution to the understanding of the attenuation phenomena of the organic contaminants off-site migration in the environment.