Occurrences, distribution and risk assessment of polar pesticides in Niger River valley and its tributary the Mekrou River (Niger Republic).

The increase in food needs due to high population growth in Niger has led to the intensification of urban agriculture and the increased use of pesticides. The objective of this study is primarily to assess the polar pesticide contamination (mainly herbicides) of the Niger River and its tributary, the Mekrou River, in Niger, using both grab sampling and POCIS (Polar Organic Chemical Integrative Samplers), and then to evaluate the risk to the aquatic environment. Two water sampling campaigns were carried out during the wet and dry seasons. The polar pesticides were analyzed by liquid chromatography coupled with tandem mass spectrometry, which allowed the identification of compounds with concentrations in the grab samples above the WHO guide values and the EU directive: diuron with 2221 ng/L (EU quality guideline: 200 ng/L), atrazine with 742 ng/L (EU quality guideline: 600 ng/L) and acetochlor with 238 ng/L (EU quality guideline: 100 ng/L). The risk assessment study indicated that diuron and atrazine present a high risk for the aquatic environment during the wet season. The main source of water contamination is the intensive use of pesticides in urban agriculture near the city of Niamey, and the intensive cotton farming in the Benin. Moreover, the surveys (30 producers interviewed) showed that 70% of the pesticides used are not approved by the Interstate Committee for Drought Control in the Sahel (CILSS) and some are prohibited in Niger. The inventory of pesticides sold in the zone showed that active ingredients used by producers are 48% insecticides, 45% herbicides, and 7% fungicides.

Study of passive sampler calibration (Chemcatcher®) for environmental monitoring of organotin compounds: Matrix effect, concentration levels and laboratory vs in situ calibration.

Application of Chemcatcher® to monitor organotin compounds [monobutyltin (MBT), dibutyltin (DBT) and tributlytin (TBT)] in sea water has been little developed. Prior to the measurement of the time-weighted average water concentrations (TWAC), a calibration step is required to determine sampling rates (Rs) which is usually assessed in a flow-through laboratory pilot where experimental conditions are well controlled. This paper investigates the effect of the water matrix (tap water vs real sea water from the harbor of Port Camargue in France) and organotin concentrations on the uptake rates of organotin compounds. Laboratory calibrations provided sampling rates in the range of 66-225 mL.day-1 in high concentration (usually used for laboratory calibrations) and in the range of 30-56 mL.day-1 at low concentrations (environmental range). When the tank is filled with real sea water, sampling rates were found to be in the range of 38-177 mL.day-1. In order to demonstrate the efficiency of Chemcatcher® in real conditions, in situ calibration was done in the harbor of Port Camargue. This calibration has been done in order to replicate environmental conditions: compounds concentrations, hydrodynamic and water matrix effects. To compare the impact of calibration procedures on TWAC determination, Chemcatcher® was deployed in the harbor of Port Camargue and spot sampling was performed to monitor the concentrations of organotins in water throughout the exposure period. Results obtained using the field Rs determined by in situ calibration were more reliable. In this case, TWAC is in agreement with spot sampling concentration.

Consequences of contaminant mixture on the dynamics and functional diversity of bacterioplankton in a southwestern Mediterranean coastal ecosystem.

Contamination of coastal environments is often due to a complex mixture of pollutants, sometimes in trace levels, that may have significant effects on diversity and function of organisms. The aim of this study was to evaluate the short-term dynamics of bacterioplankton exposed to natural and artificial mixtures of contaminants. Bacterial communities from a southwestern Mediterranean ecosystem, lagoon and the bay (offshore) of Bizerte were exposed to i) elutriate from resuspension of contaminated sediment, and ii) an artificial mixture of metals and herbicides mimicking the contamination observed during sediment resuspension. Elutriate incubation as well as artificial spiking induced strong enrichments in nutrients (up to 18 times), metals (up to six times) and herbicides (up to 20 times) relative to the in situ concentrations in the offshore station, whereas the increases in contaminants were less marked in the lagoon station. In the offshore waters, the artificial mixture of pollutants provoked a strong inhibition of bacterial abundance, production and respiration and significant modifications of the potential functional diversity of bacterioplankton with a strong decrease of the carbohydrate utilization. In contrast, incubation with elutriate resulted in a stimulation of bacterial activities and abundances, suggesting that the toxic effects of pollutants were modified by the increase in nutrient and DOM concentrations due to the sediment resuspension. The effects of elutriate and the artificial mixture of pollutants on bacterial dynamics and the functional diversity were less marked in the lagoon waters, than in offshore waters, suggesting a relative tolerance of lagoon bacteria against contaminants.