Ecotoxicological effects of diuron and chlorotoluron nitrate-induced photodegradation products: monospecific and aquatic mesocosm-integrated studies

Enhanced Biodegradation of Phenylurea Herbicides by Ochrobactrum anthrophi CD3 Assessment of Its Feasibility in Diuron-Contaminated Soils

The phenylurea herbicides are persistent in soil and water, making necessary the de-velopment of techniques for their removal from the environment. To identify new options in this regard, bacterial strains were isolated from a soil historically managed with pesticides. Ochrobactrum anthropi CD3 showed the ability to remove completely herbicides such as diuron, linuron, chlorotoluron and fluometuron from aqueous solution, and up to 89% of isoproturon. In the case of diuron and linuron, their main metabolite, 3,4-dichloroaniline (3,4-DCA), which has a higher toxicity than the parent compounds, was formed, but remained in solution without further degradation. O. anthropi CD3 was also tested for bioremediation of two different agricultural soils artificially contaminated with diuron, employing bioremediation techniques: (i) biostimulation, using a nutrient solution (NS), (ii) bioaugmentation, using O. anthropi CD3, and iii) bioavailability enhancement using 2-hydroxypropyl-β-cyclodextrin (HPBCD). When bioaugmentation and HPBCD were jointly applied, 50% of the diuron initially added to the soil was biodegraded in a range from 4.7 to 0.7 d. Also, 3,4-DCA was degraded in soil after the strain was inoculated. At the end of the soil biodegradation assay an ecotoxicity test confirmed that after inoculating O. anthropi CD3 the toxicity was drastically reduced.

Degradation of Phenylurea Herbicides by a Novel Bacterial Consortium Containing Synergistically Catabolic Species and Functionally Complementary Hydrolases

Phenylurea herbicides (PHs) are frequently detected as major water contaminants in areas where there is extensive use. In this study, Diaphorobacter sp. strain LR2014-1, which initially hydrolyzes linuron to 3,4-dichloroanaline, and Achromobacter sp. strain ANB-1, which further mineralizes the produced aniline derivatives, were isolated from a linuron-mineralizing consortium despite being present at low abundance in the community. The synergistic catabolism of linuron by the consortium containing these two strains resulted in more efficient catabolism of linuron and growth of both strains. Strain LR2014-1 harbors two evolutionary divergent hydrolases from the amidohydrolase superfamily Phh and the amidase superfamily TccA2, which functioned complementarily in the hydrolysis of various types of PHs, including linuron ( N-methoxy- N-methyl-substituted), diuron, chlorotoluron, fluomethuron ( N, N-dimethyl-substituted), and siduron. These findings show that a bacterial consortium can contain catabolically synergistic species for PH mineralization, and one strain could harbor functionally complementary hydrolases for a broadened substrate range.

Photodegradation behaviour of sethoxydim and its comercial formulation Poast® under environmentally-relevant conditions in aqueous media. Study of photoproducts and their toxicity

Photolysis is an important route for the abiotic degradation of many pesticides. However, the knowledge of the photolytic behaviour of these compounds and their commercial formulations under environmentally-relevant conditions are limited. The present study investigated the importance of photochemical processes on the persistence and fate of the herbicide sethoxydim and its commercial formulation Poast^® in aqueous media. Moreover, the effect of important natural water substances (nitrate, calcium, and ferric ions) on the photolysis of the herbicide was also studied. The results showed that additives existing in the commercial formulation Poast^® accelerated the rate of photolysis of sethoxydim by a factor of 3. On the contrary, the presence of nitrate and calcium ions had no effect on the photodegradation rate while ferric ions resulted in an important decrease in the half-life of sethoxydim possibly due to the formation of a complex. Different transformation products were identified in the course of sethoxydim irradiation and the effect of experimental conditions on their concentrations was investigated. Finally, Microtox^® test revealed that aqueous solutions of sethoxydim photoproducts increased the toxicity to the bacteria Vibrio fischeri.

Effects of a parental exposure to diuron on Pacific oyster spat methylome

Environmental epigenetic is an emerging field that studies the cause-effect relationship between environmental factors and heritable trait via an alteration in epigenetic marks. This field has received much attentions since the impact of environmental factors on different epigenetic marks have been shown to be associated with a broad range of phenotypic disorders in natural ecosystems. Chemical pollutants have been shown to affect immediate epigenetic information carriers of several aquatic species but the heritability of the chromatin marks and the consequences for long term adaptation remain open questions. In this work, we investigated the impact of the diuron herbicide on the DNA methylation pattern of spat from exposed Crassotrea gigas genitors. This oyster is one of the most important mollusk species produced worldwide and a key coastal economic resource in France. The whole genome bisulfite sequencing (WGBS, BS-Seq) was applied to obtain a methylome at single nucleotide resolution on DNA extracted from spat issued from diuron exposed genitors comparatively to control spat. We showed that the parental diuron exposure has an impact on the DNA methylation pattern of its progeny. Most of the differentially methylated regions occurred within coding sequences and we showed that this change in methylation level correlates with RNA level only in a very small group of genes. Although the DNA methylation profile is variable between individuals, we showed conserved DNA methylation patterns in response to parental diuron exposure. This relevant result opens perspectives for the setting of new markers based on epimutations as early indicators of marine pollutions.

A synthesis of the effects of pesticides on microbial persistence in aquatic ecosystems

Pesticides have a pervasive presence in aquatic ecosystems throughout the world. While pesticides are intended to control fungi, insects, and other pests, their mechanisms of action are often not specific enough to prevent unintended effects, such as on non-target microbial populations. Microorganisms, including algae and cyanobacteria, protozoa, aquatic fungi, and bacteria, form the basis of many food webs and are responsible for crucial aspects of biogeochemical cycling; therefore, the potential for pesticides to alter microbial community structures must be understood to preserve ecosystem services. This review examines studies that focused on direct population-level effects and indirect community-level effects of pesticides on microorganisms. Generally, insecticides, herbicides, and fungicides were found to have adverse direct effects on algal and fungal species. Insecticides and fungicides also had deleterious direct effects in the majority of studies examining protozoa species, although herbicides were found to have inconsistent direct effects on protozoans. Our synthesis revealed mixed or no direct effects on bacterial species among all pesticide categories, with results highly dependent on the target species, chemical, and concentration used in the study. Examination of community-level, indirect effects revealed that all pesticide categories had a tendency to reduce higher trophic levels, thereby diminishing top-down pressures and favoring lower trophic levels. Often, indirect effects exerted greater influence than direct effects. However, few studies have been conducted to specifically address community-level effects of pesticides on microorganisms, and further research is necessary to better understand and predict the net effects of pesticides on ecosystem health.