Bioaccumulation and degradation of atrazine in several Chinese ryegrass genotypes

Long-term effects of in ovo exposure to an environmentally relevant dose of atrazine on the thyroid gland of Caiman latirostris

The increased incidence of human thyroid disorders, particularly in women, suggests that the exposure to endocrine-disrupting compounds (EDCs) together with sex-related factors could play a role in thyroid dysregulation. Since the herbicide atrazine (ATZ) is an environmental EDC suspected to behave as a thyroid disruptor, and Caiman latirostris is a crocodilian species highly sensitive to endocrine disruption that can be exposed to ATZ, this study aimed to describe the histoarchitecture and sexually dimorphic features of the thyroid gland of C. latirostris, and to determine the long-term effects of in ovo exposure to an environmentally relevant dose of ATZ (0.2 ppm) on its thyroid gland and growth. Control caimans showed no sexual dimorphisms. In contrast, ATZ-exposed caimans showed altered embryo growth but an unaltered temporal pattern of development and a sexually dimorphic response in the body condition index growth curves postnatally, which suggests a female-related increase in fat storage. Besides, both male and female exposed caimans showed increases in the size of the thyroid stromal compartment, content of interstitial collagen, and follicular hyperplasia, and decreases in the expression of androgen receptor in the follicular epithelium. ATZ-exposed females, but not males, also showed evidences of thyroid enlargement, colloid depletion, increased follicular epithelial height and increased presence of microfollicular structures. Our results demonstrate that prenatal exposure of caimans to ATZ causes thyroid disruption and that females were more vulnerable to ATZ than males. The effects were organizational and observed long after exposure ended. These findings alert on ATZ side-effects on the growth, metabolism, reproduction and development of non-target exposed organisms, particularly females.

A comparison of the characteristics and atrazine adsorption capacity of co-pyrolysed and mixed biochars generated from corn straw and sawdust

The biochar used in this study was prepared from corn straw and sawdust mixed in a ratio of 1:1 (m/m) at temperatures of 300 °C and 800 °C, which adopted the methods of co-pyrolysis (BC_300A and BC_800A) and mixing of single biochar (BC_300B and BC_800B). The obtained biochar was characterized by SEM, BET and FTIR analysis. Adsorption properties, including the atrazine adsorption kinetics and isotherms of the four kinds of biochar to atrazine, were investigated. The results showed that a pseudo-second order kinetic model was suitable for describing the adsorption of atrazine by BC_800B because its R² value is greater than the pseudo-first order model. The adsorption capacity (q_e) of BC_800B, blended from the two single biochars produced at 800 °C, is 37.2 mg g^-1, which is better than that of the other three species. This value is 4-6 times the q_e values of BC_300A, BC_300B and BC_800A, which are 6.74 mg g^-1, 7.77 mg g^-1 and 5.26 mg g^-1, respectively. At higher pyrolysis temperature, the pore structure of biochar is more developed, the specific surface area is larger, and the species and number of surface functional groups are also significantly different. At the same time, the results also showed that the order of mixing and pyrolysis affected the characteristics and adsorption capacity of biochar. This study reveals the atrazine adsorption mechanism of four kinds of biochar and provides information about the potential of these types of materials for the removal of atrazine in the aquatic environment.

Reduced phytotoxicity of propazine on wheat, maize and rapeseed by salicylic acid

Propazine belongs to the triazine herbicide family and widely used in the farmland for crop production. Recent studies have shown that the residue of propazine in environment is accumulative. This inevitably results in accumulation of propazine in crops. Therefore, reduction of propazine toxicity and accumulation in crops is critically important. In this study, the growth of wheat, maize and rapeseed was significantly inhibited by 2, 8 and 0.4 mg kg^-1 propazine in soils. The chlorophyll content of the three crops also showed significant decrease, while the electrolyte permeability, a biomarker of cellular damage, increased in the plant cells. However, when plants were sprayed with 5 mg L^-1 of salicylic acid (SA), the propazine phytotoxicity of the crops was relieved, with increased chlorophyll content and reduced electrolyte permeability of all crops. Meanwhile, the activities of peroxidase (POD) and glutathione transferase (GST) remained lower. The propazine accumulation in the crops and the residues in the soil were determined by high performance liquid chromatography. The concentration of propazine in plants and soils treated by SA was less than that of the untreated control. Six propazine degraded products (derivatives) in rhizosphere of wheat were characterized using ultraperformance liquid chromatography with a quadrupole-time-of-flight tandem mass spectrometer. Our work indicates that the improved growth of crops was possibly due to the acceleration of propazine degradation by salicylic acid.

The enhancement of atrazine sorption and microbial transformation in biochars amended black soils

Generally, biochar plays an important role in controlling migration and accumulation of pollutants in soil. In this dissertation, biochars derived from wheat straws at various pyrolysis temperatures are used to investigate how biochar amendment affects adsorption and microbial degradation of atrazine (typical diffuse herbicide) in soils. In order to explore the influence of soil components, soil samples with different organic matter content are collected from typical agricultural sites, which are characterized as black soils in the northeast region of China. The basic sorption characteristics of biochars from wheat straws prepared at diverse pyrolysis temperature are analyzed, along with the comparisons of the sorption difference in the raw soil and soil amended with biochars at four levels of ratio (0.1%, 0.5%, 1.0% and 2.0%). By incubation experiments, atrazine degradation in non-sterile and sterile soils and effects of atrazine degradation rate after biochar amendment are also studied. Atrazine degradation is significantly enhanced in biochar amended soils, which may be because that biochar supplement can promote the growth and metabolism of microorganisms in the soil. Our findings reveal that wheatstraw- derived biochars may be effective remediation reagents for activating degradation of the soil functional microorganism and enhancing sorption of organic matter content, which can be applied to environmental-friendly accelerate the remediation of atrazine contaminated black soils.

Activity, biomass and composition of microbial communities and their degradation pathways in exposed propazine soil

Propazine is a s-triazine herbicide widely used for controlling weeds for crop production. Its persistence and contamination in environment nagatively affect crop growth and food safety. Elimination of propazine residues in the environment is critical for safe crop production. This study identified a microbial community able to degrade propazine in a farmland soil. About 94% of the applied propazine was degraded within 11 days of incubation when soil was treated with 10mgkg^-1 propazine as the initial concentration. The process was accompanied by increased microbial biomass and activities of soil enzymes. Denaturing gradient gel electrophoresis (DGGE) revealed multiple bacterial strains in the community as well as dynamic change of the composition of microbial community with a reduced microbial diversity (H' from 3.325 to 2.78). Tracking the transcript level of degradative genes AtzB, AtzC and TrzN showed that these genes were induced by propazine and played important roles in the degradation process. The activities of catalase, dehydrogenase and phenol oxidase were stimulated by propazine exposure. Five degradation products (hydroxyl-, methylated-, dimeric-propazine, ammeline and ammelide) were characterized by UPLC-MS², revealing a biodegradation of propazine in soil. Several novel methylated and dimeric products of propazine were characterized in thepropazine-exposed soil. These data help understand the pathway, detailed mechanism and efficiency of propazine biodegradation in soil under realistic field condition.

Comprehensive analysis of degradation and accumulation of ametryn in soils and in wheat, maize, ryegrass and alfalfa plants

Ametryn is a selective herbicide belonging to the triazine family and widely used for killing annual grasses or weeds in China and other parts of the world. However, reports on its environmental risk assessment with regard to soil and crop contamination are limited. In this study, accumulation of ametryn in wheat, maize, ryegrass and alfalfa crops along with ametryn residues in the soil planted with the plants were comparatively investigated. Soil enzyme activities and low molecular weight organic acids (LMWOAs), as well as antioxidant and degradation enzyme activities in plant tissues were measured. The maximum accumulation of ametryn was found in shoots and roots of wheat and alfalfa. Ryegrass had the maximum ametryn translocation factor (TF) from roots to shoots, with more than three times over the other crops. The ametryn residue in ryegrass-planted soil was much lower than that in soil planted with others. The residual content of ametryn in crop-planted soils was ordered as rhizosphere soil<bulk soil<non-rhizosphere soil<control (without plants). Activities of catalase (CAT), glutathione S-transferase (GST) and laccase (LAC) in ametryn-exposed ryegrass were significant higher than those in non-ametryn exposed ryegrass. The maximum activities of CAT in ryegrass shoot and root were increased by 6.16- and 28.84-fold over the control, respectively. Exudation of organic acids in the crop was induced by ametryn and contributed a lot to the degradation of the herbicide. Thus, ryegrass was shown to have a relatively strong ability to remove ametryn from ametryn-contaminated soil and its plant tissues as well.

Rice (Oryza sativa) Laccases Involved in Modification and Detoxification of Herbicides Atrazine and Isoproturon Residues in Plants

Atrazine (ATR) and isoproturon (IPU) as herbicides have become serious environmental contaminants due to their overuse in crop production. Although ATR and IPU in soils are easily absorbed by many crops, the mechanisms for their degradation or detoxification in plants are poorly understood. This study identified a group of novel genes encoding laccases (EC 1.10.3.2) that are possibly involved in catabolism or detoxification of ATR and IPU residues in rice. Transcriptome profiling shows at least 22 differentially expressed laccase genes in ATR/IPU-exposed rice. Some of the laccase genes were validated by RT-PCR analysis. The biochemical properties of the laccases were analyzed, and their activities in rice were induced under ATR/IPU exposure. To investigate the roles of laccases in degrading or detoxifying ATR/IPU in rice, transgenic yeast cells (Pichia pastoris X-33) expressing two rice laccase genes (LOC_Os01g63180 and LOC_Os12g15680) were generated. Both transformants were found to accumulate less ATR/IPU compared to the control. The ATR/IPU-degraded products in the transformed yeast cells using UPLC-TOF-MS/MS were further characterized. Two metabolites, hydroxy-dehydrogenated atrazine (HDHA) and 2-OH-isopropyl-IPU, catalyzed by laccases were detected in the eukaryotic cells. These results indicate that the laccase-coding genes identified here could confer degradation or detoxification of the herbicides and suggest that the laccases could be one of the important enzymatic pathways responsible for ATR/IPU degradation/detoxification in rice.

Identification of transcriptome involved in atrazine detoxification and degradation in alfalfa (Medicago sativa) exposed to realistic environmental contamination

Plants are constantly exposed to a variety of toxic compounds (or xenobiotics) such as pesticides (or herbicides). Atrazine (ATZ) as herbicide has become one of the environmental contaminants due to its intensive use during crop production. Plants have evolved strategies to cope with the adverse impact of ATZ. However, the mechanism for ATZ degradation and detoxification in plants is largely unknown. Here we employed a global RNA-sequencing (RNA-Seq) strategy to dissect transcriptome variation in alfalfa (Medicago sativa) exposed to ATZ. Four libraries were constructed including Root-ATZ (root control, ATZ-free), Shoot-ATZ, Root+ATZ (root treated with ATZ) and Shoot+ATZ. Hierarchical clustering was performed to display the expression patterns for all differentially expressed genes (DEGs) under ATZ exposure. Transcripts involved in ATZ detoxification, stress responses (e.g. oxidation and reduction, conjugation and hydrolytic reactions), and regulations of cysteine biosynthesis were identified. Several genes encoding glycosyltransferases, glutathione S-transferases or ABC transporters were up-regulated notably. Also, many other genes involved in oxidation-reduction, conjugation, and hydrolysis for herbicide degradation were differentially expressed. These results suggest that ATZ in alfalfa can be detoxified or degraded through different pathways. The expression patterns of some DEGs by high-throughput sequencing were well confirmed by qRT-PCR. Our results not only highlight the transcriptional complexity in alfalfa exposed to ATZ but represent a major improvement for analyzing transcriptional changes on a large scale as well.