Sylvie Dousset

Isolation and characterisation of Nocardioides sp. SP12, an atrazine-degrading bacterial strain possessing the gene trzN from bulk- and maize rhizosphere soil

We report the characterisation of Nocardioides sp. SP12, an atrazine-degrading bacteria isolated from atrazine-treated bulk- and maize rhizosphere soil. Based on 16S rDNA alignment, strain SP12 showed close phylogenic relationships with Nocardioides sp. C157 and Nocardioides simplex. Internal transcribed spacer (ITS) sequences of strain SP12 were longer than those of other Nocardioides sp. and present Ala- and Ile-tRNA unlike Actinomycetales. Nocardioides sp. SP12 presents a novel atrazine catabolic pathway combining trzN with atzB and atzC. Atrazine biodegradation ends in a metabolite that co-eluted in HPLC with cyanuric acid. This metabolite shows an absorption spectrum identical to that of cyanuric acid with a maximal absorption at 214.6 nm. The mass of the atrazine metabolite is in concordance with that of cyanuric acid according to mass spectrometry analysis. Quantitative PCR revealed that the ITS sequence of Nocardioides sp. SP12 was at a lower number than the one of trzN in atrazine-treated soil samples. It suggests that trzN could also be present in other atrazine degrading bacteria. The numbers of trzN and ITS sequences of Nocardioides sp. SP12 were higher in the maize rhizosphere than in bulk soil.

Sorption of terbuthylazine and atrazine in relation to the physico-chemical properties of three soils

Abstract The adsorption and desorption of the herbicides atrazine and terbuthylazine in loamy clay, calcareous clay and high clay soils were studied using a batch equilibration method. The main differences between soils were the clay content, 31.7%, 51.3% and 62.5% for the loamy clay, the calcareous clay and the high clay soils, respectively, and the organic carbon content, 1.11%, 1.50% and 1.08%, respectively. Adsorption and desorption isotherms were well described by the Freundlich equation. Terbuthylazine was more adsorbed (Freundlich K f coefficient ranged from 1.88 to 2.33) than atrazine (K f ranged from 0.96 to 1.22) by the three soils. The desorption studies showed that the bondings between terbuthylazine and soil were less reversible than those of atrazine. The adsorption of these triazines was not related to clay or organic carbon contents, but to the degree of humification of the organic matter.

Degradation of [14C]terbuthylazine and [14C]atrazine in laboratory soil microcosms

The degradation and formation of major chlorinated metabolites of terbuthylazine and atrazine in three soils (loamy clay, calcareous clay and high clay) were studied in laboratory experiments using molecules labelled with 14C on the s-triazine ring. Soil microcosms were treated with the equivalent of 1 kg ha-1 of herbicide and incubated in the dark for 45 days at 20(±1)°C. The quantity of [14C]carbon dioxide evolved in the soils treated with atrazine was negligible and could not be attributed to mineralization of the parent molecule. The mineralization of terbuthylazine accounted for 0·9–1·2% of the initial radioactivity. In the soils studied, the extrapolated half-lives varied from 88 to 116 days for terbuthylazine and 66 to 105 days for atrazine, with no significant differences for the three soils and the two molecules. The deethyl metabolites of the two s-triazines and the deisopropyl-atrazine metabolite appeared during the incubation in the three soils. The completely dealkylated metabolite was not detected in any of the soils. After 45 days of incubation, the non-extractable soil residues for the high clay, loamy clay and calcareous clay soils represented for terbuthylazine, 33·5, 38·3 and 43·1% and for atrazine, 19·8, 20·8 and 22·3% of the initial radioactivity.

Interactions of diuron with dissolved organic matter from organic amendments.

Diuron is frequently detected in some drinking water reservoirs under the Burgundy vineyards, where organic amendments are applied. The environmental effect of these amendments on pesticide transport is ambiguous: on the one hand it could enhance their retention by increasing soil organic carbon content; on the other hand, dissolved organic matter (DOM) could facilitate their transport. Elutions were performed using columns packed with glass beads in order to investigate DOM-diuron interactions, and the possible co-transport of diuron and DOM. Four organic amendments (A, B, C and D) were tested; C and D were sampled at fresh (F) and mature (M) stages. An increase in diuron leaching was observed only for A and D(F) amendments (up to 16% compared to the DOM-free blank samples), suggesting a DOM effect on diuron transport. These results could be explained by the higher DOM leaching for A and D(F) compared to B, C(F), C(M) and D(M) increasing diuron-DOM interactions. These interactions seem to be related to the aromatic and aliphatic content of the DOM, determining formation of hydrogen and non-covalent bonds. The degree of organic matter maturity does not seem to have any effect with amendment C, while a reduction in diuron leaching is observed between D(F) and D(M). After equilibrium dialysis measurement of diuron-DOM complexes, it appeared that less than 3% of the diuron applied corresponded to complexes with a molecular weight >1000 Da. Complexes <1000 Da could also take part in this facilitated transport.

Leaching of atrazine and some of its metabolites in undisturbed field lysimeters of three soil types

The movement of 14C-atrazine was studied in lysimeters (10×70 cm) under field conditions in loamy clay, calcareous clay and a high clay soils. Ten months after atrazine treatment and with a cumulative rainfall of 502 mm, the leachates from the calcareous clay soil contained 3.3% of applied s-triazine radioactivity, while those from the loamy clay and high clay soils contained only 0.9% and 1.1%, respectively. The mobility of the s-triazine residues was not related to the distribution of organic carbon content withh depth. The proportion of extractable residues in the upper levels of the lysimeters was lower for the calcareous clay soil, 19.2% compared to 30.0 and 28.6% in the loamy clay and high clay soils. The extraclable residues increased with depth in the calcareous clay soil, 62.8% in the 54-60 cm layer, whereas it decreased in the loamy clay and high clay soils down to 16.3 and 17.6%, respectively. Atrazine was observed to a depth of 36 cm in the loamy clay and high clay soils, and to a depth of 54 cm in the calcareous clay soil. Diamino-atrazine was detected in some places while deethyl-atrazine and deisopropyl-atrazine were present over a large part of the soil profile, sometimes to depths greater than that of the parent molecule. The results suggest a greater mobility of the s-triazine residues in the calcareous clay soil.

Insecticide residues in cotton soils of Burkina Faso and effects of insecticides on fluctuating asymmetry in honey bees (Apis mellifera Linnaeus)

Four insecticides (acetamiprid, cypermethrin, endosulfan and profenofos) are used quarterly in the cotton-growing areas of Burkina Faso, West Africa. These insecticides were investigated in soils collected from traditionally cultivated and new cotton areas. Also, the effects of insecticide exposure on the developmental instability of honey bees, Apis mellifera, were explored. In soil samples collected three months after insecticide treatments, endosulfan and profenofos concentrations varied in the range of 10-30 μg kg(-1) in the traditionally cultivated zones and 10-80 μg kg(-1) in the new cotton zones, indicating a pollution of agricultural lands. However, only profenofos concentrations were significantly higher in the new cotton zone than the traditionally cultivated zones. In addition, the index of fluctuating asymmetry, FA1, in the length of second tarsus (L(HW)) was increased for bees when exposed to pesticide treated cotton fields for 82d, and their FA levels were significantly higher than those in the control colony in an orchard. The other studied traits of bees exposed to insecticides were not significantly different from controls. Our results indicate that FA may be considered as a biomarker reflecting the stress induced by insecticide treatments. However, the relationship between FA and stressors needs further investigations.

Effect of grass cover on water and pesticide transport through undisturbed soil columns, comparison with field study (Morcille watershed, Beaujolais).

The purpose of this work is to assess the effectiveness of two grass covers (buffer zone and grass-covered inter-row), to reduce pesticide leaching, and subsequently to preserve groundwater quality. Lower amounts of pesticides leached through grass-cover soil columns (2.7-24.3% of the initial amount) than the bare soil columns (8.0-55.1%), in correspondence with their sorption coefficients. Diuron was recovered in higher amounts in leachates (8.9-32.2%) than tebuconazole (2.7-12.9%), in agreement with their sorption coefficients. However, despite having a sorption coefficient similar to that of diuron, more procymidone was recovered in the leachates (10.2-55.1%), probably due to its facilitated transport by dissolved organic matter. Thus even in this very permeable soil, higher organic matter contents associated with grass-cover reduce the amount of pesticide leaching and limit the risk of groundwater contamination by the pesticides. The results of diuron and tebuconazole transfer through undisturbed buffer zone soil columns are in agreement with field observations on the buffer zone.

Adsorption of isoproturon on homoionic clays

The adsorption of isoproturon (3-(4-isopropylphenyl)- 1,1 dimethylurea)] on a montmorillonite and on a kaolinite was studied by batch experiments and Fourier transform infrared spectroscopy (FT-IR). The clays were saturated with cations such as Al3+, Ca2+, Cu2+, Na+ and hexadecyl-trimethylammonium (HDTMA). The studied clays did not show detectable catalytic activity on abiotic degradation of isoproturon, as evidenced by HPLC analysis. Adsorption was found related to clay specific external surface for HDTMA-saturated clays, while it seems independent from clay kind and inorganic cation. For clays saturated with inorganic cations, no penetration into the mont-morillonite interlayer was found and FT-IR spectroscopy showed the involvement of CO group of isoproturon in adsorption.

Leaching of Diuron, Linuron and their main metabolites in undisturbed field lysimeters

The increasing use of pesticides in Morocco raises the potential risk of groundwater contamination, notably in the Gharb area, which has a shallow groundwater table. Thus, the leaching of two phenyl-ureas, diuron and linuron and their metabolites through undisturbed soil columns was studied under outdoor conditions. The soil chosen is a loamy clay soil, representative of the Gharb agricultural area. After four irrigation events were applied from 31/03/2005 to 15/05/2005, leachates contained higher amounts of linuron (from 0.08% to 6.96% of applied linuron) than diuron (from 0% to 0.27%). The greater mobility of linuron might be related to its higher water solubility (64 mg · L− 1 compared with 42 mg · L− 1 for diuron) and smaller adsorption coefficient (Koc of 400 L · kg− 1, compared with 480 L · kg− 1 for diuron). Concerning their metabolites, greater amounts of, N′-(3,4-dichlorophenyl)-N, (DCPMU) than N′-3,4-dichlorophenylurea (DCPU) were detected N-dimethylurea in the percolates, from 0% to 0.046% and from 0% to 0.008%, respectively. At the end of the monitoring period, more linuron residues than diuron residues were recovered in the soil profiles, 25.02% and 16.41%, respectively. The diuron residues were found mainly in the 0-20 cm soil layer, whereas linuron residues reached the 20-40 cm soil layer. Under such experimental conditions, linuron leaching, and thus its potential to contaminate groundwater, is greater than that of diuron.

Effectiveness of vetiver grass (Vetiveria zizanioides L. Nash) for phytoremediation of endosulfan in two cotton soils from Burkina Faso.

The influence of vetiver grass (Vetiveria zizanioides) on the fate of endosulfan was studied using a vertisol and a lixisol soils from cotton-growing areas of Burkina Faso. Endosulfan adsorption isotherms were prepared for planted and unplanted soils. Pot experiments were then conducted for six months. For both soils, endosulfan adsorption was higher on planted soils (Kf= 6.53–9.73 mg1–nLnkg–1) than on unplanted soils (6.27–7.24 mg1–nLnkg–1). In unplanted soils, vertisol adsorbed more endosulfan than lixisol. From the pot experiments, the estimated half-lives of endosulfan in unplanted soils (40.6 to 43.1 days) were higher than in planted soils (34.5 to 40.6 days) containing a greater number of endosulfan-degrading microorganisms. Six months after treatment, endosulfan was not detected in soils. The effectiveness of vetiver in promoting adsorption and the disappearance of endosulfan in both studied soils should be validated on the cotton plot scale in Burkina Faso.