Effect of salinity on the fate of pesticides in irrigated systems: a first overview

International audienceThis review investigates the impact of salinity on the fate of the active compounds of pesticides in a cultivated environment. Due to the over-exploitation of water resources and intensification of agriculture, salinity outbreaks are being observed more often in cultivated fields under pesticide treatments. Nevertheless, there is a poor understanding of the incidence of varying water salt loads on the behavior of pesticides’ active ingredients in soil and water bodies. The present review established that water salinity can affect the diffusion of pesticides’ active ingredients through numerous processes. Firstly, by increasing the vapor pressure and decreasing the solubility of the compounds, which is known as the salting-out effect, salinity can change the colligative properties of water towards molecules and the modification of exchange capacity and sorption onto the chemicals. It has also been established that the osmotic stress induced by salinity could inhibit the biodegradation process by reducing the activity of sensitive microorganisms. Moreover, soil properties like dissolved organic matter, organic carbon,clay content, and soil texture control the fate and availability of chemicals in different processes of persistence in water and soil matrix. In the same line, salinity promotes the formation of different complexes, such as between humic acid and the studied active compounds. Furthermore, salinity can modify the water flux due to soil clogging because of the coagulation and dispersion of clay particle cycles, especially when the change in salinity ranges is severe

The use of IRPeQ model as indicator to estimate the risk of some pesticides on human health and environment. Bouagga, A., Chaabane, H., Bahrouni, H., and Hassine K

Different pesticides can be used by farmers to control bioagressors. To assess environmental and human health risks due to pesticide use, pesticide risk indicators are elaborated. The objective of this study was to characterize the potential risks of pesticides used and their side effects on health and environment. A census of the use of pesticides in citrus orchards was conducted among farmers in Tunisia during crop season 2013/14. Two risk indexes were calculated for each pesticide: a Health Risk Index (HRI) and an Environmental Risk Index (ERI) according to the Quebec Pesticides Risk Indicator (IRPeQ). The parameters used to follow each calculation were obtained from the registration dossier of each formulation and the international databases like Agritox, Extoxnet and PAN Pesticides. The highest HRI were obtained for the formulations based on the active ingredient methidathion (HRI= 1227), while, Success Appât ® a formulation, based on spinosad as active ingredient, is the product with the lowest health risk (HRI= 12). On the other hand, its ERI was evaluated with an index of 175, according to its toxicity towards honey bees. The fungicide formulation Aliette Express® presented slightly low health and environmental risk indexes. The determination of the risk indexes HRI and ERI allowed us to compare pesticides (active ingredient and formulation) according to their potential risk and facilitate the choice of the pesticide with least risk for human health and environment

Rigid ryegrass (Lolium rigidum) abundance in Tunisian Northern cereal fields and its susceptibility to selected inhibitors of acetolactate synthase (ALS) and acetyl coenzyme A carboxylase (ACCase). Khammassi, M., Chaabane, H., Bousselmi, A., Belbahri, N., and Souissi, T. (Tunisia)

Rigid ryegrass (Lolium rigidum) is one of the most prevalent grass weed in cereal crops in Tunisia. The study was undertaken to determine its occurrence in the Northern regions of the country and to evaluate its susceptibility to selected commonly used herbicides inhibitors of acetyl Coenzyme A carboxylase (ACCase) and acetolactate synthase (ALS). The frequency of infested surveyed fields by this weed is 32%. Its abundance varied among locations and bioclimatic stages. High weed infestations (> 300 individuals/m²) were located in the Northern regions of Bizerte and Bejà where weather conditions, namely the rainfall, are the most favorable. None of the tested herbicides whether in field trials or in pot experiment gave a satisfactory control of rigid ryegrass. Over 80% of tested ryegrass populations in pots were resistant to clodinafop-propargyl and iodo-mesosulfuron, with high proportions of resistant plants to both tested herbicides, suggesting that rigid ryegrass has evolved resistance to herbicides commonly used to control weeds in wheat fields

Tuberculous meningitis in adults: MRI contribution to the diagnosis in 29 patients

SummaryObjectivesTuberculous meningitis (TBM) is a life-threatening disease and is difficult to diagnose. We aim to promote the role of magnetic resonance imaging (MRI) in TBM diagnosis and survey.Design and methodsThis was a retrospective study undertaken between 1996 and 2003 in which we reviewed all cases of TBM that had undergone cerebral computed tomography (CT) and MRI performed with and without contrast.ResultsWe reviewed 29 patients; all had had subacute lymphocytic meningitis. Diagnosis was definite in only 11 cases and presumptive in 18 cases. MRI was performed showing one or more abnormalities in 26 cases. The use of MRI allowed the detection of CNS lesions in both brain and spine.ConclusionCerebrospinal MRI performed when TBM is suspected aids in its diagnosis and is also a useful means of monitoring the course of the disease under treatment

Photodegradation of sulcotrione in various aquatic environments and toxicity of its photoproducts for some marine micro-organisms.

International audiencePhotochemical behaviour of sulcotrione, a triketone herbicide, was studied in a variety of aqueous solutions including natural waters (sea and river) under laboratory conditions. Photodegradation experiments were carried out under two irradiation systems (UV-B and simulated solar radiation) in order to evaluate kinetics of active ingredient. The degradation kinetics, more rapid under UV-B radiation than solar simulator, followed a first-order reaction (photolysis half-lives ranged between 3 and 50 h) and appeared strongly dependent on water origin, pH value and molecular structure of the herbicide. Dissolved organic matter showed a retarding effect while low concentrations of nitrate ions had no effect on photolysis rate. Identification of photoproducts indicated that hydrolysis, a pH-dependent process (no degradation at pH >6 but at pH=3, k=0.0344 h(-1)), could be photoassisted. These results were compared to those of mesotrione, another triketone herbicide, which appeared more stable under UV-B irradiation. Toxicological studies on two marine heterotrophic bacteria and one cyanobacterium showed absence of effects up to 100 microgL(-1) for both sulcotrione and its photoproducts

Environmental Fate of the Insecticide Chlorpyrifos in Soil Microcosms and Its Impact on Soil Microbial Communities

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Genetic diversity and population structure of Zymoseptoria tritici on bread wheat in Tunisia using SSR markers

Septoria tritici blotch (STB) caused by Zymoseptoria tritici is the primary biotic stress for durum wheat production in Tunisia. The present study was aimed to decipher the genetic diversity and population structure of Z. tritici bread wheat isolates; in the northern regions of Tunisia this pathogen infected exclusively bread wheat. A total of 162 single-spore isolates were sampled during the 2015–2016 growing season from nine naturally infected bread wheat fields at four locations in the three main wheat-growing regions in Tunisia, previously reported as hot spots for Septoria disease (Cap Bon, Bizerte, and Beja). Collected isolates were fingerprinted using twelve polymorphic microsatellite markers to assess the genetic diversity and population structure of Z. tritici. All the microsatellite loci were polymorphic and a high genetic diversity was observed within the whole population. The highest Nei’s index value (0.42), Shannon Index (0.84) and private allele numbers (36) were found at the El Haouaria location (Cap Bon region). Furthermore, a moderate genetic differentiation within and among the surveyed locations (73% and 27%) was confirmed by analysis of molecular variance (AMOVA). On the other hand, the STRUCTURE program was shown to be less sensitive in revealing genetic structure especially at low levels of diversity. Thus, information on the genetic structure of the pathogen population collected from bread wheat is useful for designing and implementing durable and effective management strategies

Genetic diversity and population structure of Zymoseptoria tritici on bread wheat in Tunisia using SSR markers

Septoria tritici blotch (STB) caused by Zymoseptoria tritici is the primary biotic stress for durum wheat production in Tunisia. The present study was aimed to decipher the genetic diversity and population structure of Z. tritici bread wheat isolates; in the northern regions of Tunisia this pathogen infected exclusively bread wheat. A total of 162 single-spore isolates were sampled during the 2015–2016 growing season from nine naturally infected bread wheat fields at four locations in the three main wheat-growing regions in Tunisia, previously reported as hot spots for Septoria disease (Cap Bon, Bizerte, and Beja). Collected isolates were fingerprinted using twelve polymorphic microsatellite markers to assess the genetic diversity and population structure of Z. tritici. All the microsatellite loci were polymorphic and a high genetic diversity was observed within the whole population. The highest Nei’s index value (0.42), Shannon Index (0.84) and private allele numbers (36) were found at the El Haouaria location (Cap Bon region). Furthermore, a moderate genetic differentiation within and among the surveyed locations (73% and 27%) was confirmed by analysis of molecular variance (AMOVA). On the other hand, the STRUCTURE program was shown to be less sensitive in revealing genetic structure especially at low levels of diversity. Thus, information on the genetic structure of the pathogen population collected from bread wheat is useful for designing and implementing durable and effective management strategies