Effects of some phenylamide herbicides and their degradation products on soil nitrification

State of the art of the environmental behaviour and removal techniques of the endocrine disruptor 3,4-dichloroaniline

In recent years, the presence of Endocrine Disrupting Chemicals (EDCs) in wastewater discharges from agricultural and industrial sources, ^[1] fresh- and estuarine-waters, as well as soils, has been reported in the literature. ^[2] Studies of adverse changes in wildlife, linked to environmental exposure to these substances, and the suggestion that humans could also be at similar risk of adverse health effects, ^[3-5] have raised concern for urgent action to understand and reduce such risks. 3,4-Dichloroaniline (3,4-DCA) has been recognized as an EDC, with regards to endocrine disruption data for both wildlife populations and human health. ^[5] 3,4-DCA is present in the environment as a product of the biodegradation of phenylurea and phenylcarbamate pesticides ^[6,7] ; furthermore, it can be introduced from industrial and municipal wastewater that is insufficiently purified, or via accidental spills. ^[8-10] Increasing concentrations of 3,4-DCA in soil and water are the result of its high persistence and accumulation, as well as its low biodegradability. ^[11,12] Hence, remediation techniques require in-depth study, especially when considering the low removal achieved by traditional activated sludge treatments, and the generation of carcinogenic trihalomethanes as a consequence of the chlorine oxidation methods frequently used in drinking water plants. ^[13] Fe⁰/H₂O₂ systems, photodegradation using doped TiO₂, and the use of dielectric barrier discharge reactors, seem to be the most promising techniques for the removal of 3,4-DCA from water.

Effect of three organophosphorous nematicides on non-target nematodes and soil microbial community

The toxicity of three organophosphorous nematicides, imicyafos, fosthiazate and cadusafos, to non-target organisms in soil was evaluated. Imicyafos and fosthiazate had no significant inhibitory effect on the growth of fungal (Fusarium oxysporum f. sp. lactucae, Rhizoctonia solani and Trichoderma viride) and bacterial (Ralstonia solanacearum and Pseudomonas fluorescens) strains in media at 12.5 to 200 mg L(-1). Cadusafos, however, significantly inhibited the growth of all these strains except R. solanacearum. A pot test was conducted using a soil naturally infested with Pratylenchus penetrans, and treated with imicyafos or fosthiazate, which are less toxic to non-target organisms. The density of P. penetrans decreased to less than 10% of the control level after exposure to imicyafos and fosthiazate at 3 kg active ingredient ha(-1), the conventional dose. No significant effect was observed on the density of free-living nematodes, cellulose decomposition activity, microbial biomass evaluated with the ATP method and number of ammonia oxidizers between the soil treated with imicyafos or fosthiazate and the untreated control soil. Our results revealed that imicyafos and fosthiazate effectively suppressed a plant-parasitic nematode, P. penetrans, but had little impact on free-living nematodes and the soil microbial community.

Nitrite and nitrous oxide accumulation during denitrification in the presence of pesticide derivatives

Temporary accumulation of nitrite and nitrous oxide was observed in soil incubated under anaerobic conditions when derivatives of the insecticide chlordimeform [(N-4-chloro-o-tolyl)-N',N' -dimethylformamidine] were added. Chlordimeform did not affect the denitrification process, but N-formyl-4-chloro-o-toluidine and 4-chloro-o-toluidine caused an inhibition as determined by the accumulation of nitrite and nitrous oxide. A simultaneous application of the insecticide and its derivatives resulted in a stronger inhibitory effect than the application of each compound separately. Aniline intermediates of other pesticides also inhibited denitrification in soil, and they proved to be more effective than their parent compound.

Herbicides and soil microorganisms

The production and usage of herbicides have increased dramatically in recent years. Consequently there is growing concern about the effects of these chemicals on the environment, particularly the possible long-term effects on soil fertility which may result from disturbance of the soil microflora. This review considers the recent developments in the study of the interactions between herbicides and microorganisms, and discusses the problems of evaluating the results of such studies with a view to determining or predicting possible short-term or long-term effects which may be of practical significance.