Occurrence, distribution and ecological risk assessment of the herbicide simazine: A case study

Enhanced simazine degradation via peroxymonosulfate activation using hemin-doped rice husk biochar as a novel Fe/N-C catalyst

The presence of herbicides, including simazine (SIM), in aquatic environments pose significant threats to these ecosystems, necessitating a method for their removal. In this study, a hemin-doped rice husk-derived biochar (RBC@Hemin20%) was synthesized using a simple, one-step pyrolysis, and its degradation efficiency towards SIM via peroxymonosulfate (PMS) was assessed. Under optimized conditions (hemin loading = 20 wt%, SIM = 0.5 ppm, RBC@Hemin20% catalyst = 0.2 g L-1, PMS = 2.0 mM, and pH = 5.84 [unadjusted]), RBC@Hemin20%, as an Fe/N-C catalyst, could activate PMS to achieve >99% degradation of SIM. Based on radical scavenger and electron spin resonance spectroscopy (ESR) experiments, both radical (•OH and SO4•-) and non-radical (such as singlet oxygen, 1O2) mechanisms and electron transfer were involved in the degradation system. Significant mineralization (97.3%) and reusability efficiency (∼74.1% SIM degradation after 4 applications) were exhibited by the RBC@Hemin20%/PMS system, which also maintained a remarkable degradation efficiency in tap-, river-, and ground-water. Additionally, the RBC@Hemin20%/PMS system exhibited rapid degradation of tetracycline (TC) and diclofenac (DCF), indicating its prospects in the degradation of other organic pollutants of aquatic environments. The plausible degradation mechanism pathways of SIM are proposed based on identified intermediates. Finally, the toxicity of these intermediate products is analysed using the Ecological Structure Activity Relationship (ECOSAR) software. It is expected that this study will expand the current knowledge on the synthesis of efficient biomass-based Fe/N-C composites for the removal of organic pollutants in water.

Highly selective molecularly imprinted-electrochemiluminescence sensor based on perovskite/Ru(bpy)32+ for simazine detection in aquatic products

A novel molecularly imprinted electrochemiluminescence (MIECL) sensor based on the luminescence of molecularly imprinted polymer-perovskite (MIP-CsPbBr₃) layer and Ru(bpy)₃²⁺ was fabricated for simazine detection. MIP-CsPbBr₃ layers were immobilized onto the surface of glassy carbon electrode as the capture and signal amplification probe, and Ru(bpy)₃²⁺ and co-reactant tripropylamine exhibited stronger electrochemiluminescence (ECL) emission. Under optimal conditions, the ECL signal of the MIECL sensor was linearly quenched, with the logarithm of simazine concentration ranging from 0.1 μg/L to 500.0 μg/L, correlation coefficient of 0.9947, and limit of detection of 0.06 μg/L. The practicality of the developed MIECL sensor method for simazine determination in aquatic samples was validated. Excellent recoveries of 86.5 %-103.9 % with relative standard deviation below 1.6 % were obtained for fish and shrimp samples at three different spiked concentrations. The MIECL sensor exhibited excellent selectivity, sensitivity, reproducibility, accuracy, and precision for simazine determination in actual aquatic samples.

The toxicokinetics and risk assessment of pyrethroids pesticide in tilapia (Oreochromis mossambicus) upon short-term water exposure

Pyrethroids pesticides (PPs) are the widely adopted synthetic pesticides for agriculture and fishery. The frequent use of these pesticides leads to the accumulation of residues in the freshwater environments in China, subsequently affecting aquatic organisms and ecosystems. However, there are few reports on the toxicological and risk assessment of aquaculture aquatic products. In this study, the uptake, depuration kinetics and potential risk to human health and ecology of fenpropathrin, cypermethrin, fenvalerate, and deltamethrin were assessed using tilapia. The results indicated that four PPs were readily accumulated by tilapia. The bioconcentration factors (BCF) of the PPs in plasma and muscle were between 71.3 and 2112.1 L/kg and 23.9-295.3 L/kg, respectively. The half-lives (t_1/2) of muscle and plasma were 2.90-9.20 d and 2.57-8.15 d. The risks of PPs residues in the muscle of tilapia and exposed water were evaluated by hazard quotient (HQ) and risk quotient (RQ). Although PPs residues in tilapia had a low dietary risk to human health, the residues in the exposed water had a high ecological risk to fish, daphnia, and green algae. Therefore, assessing the PPs content in freshwater aquaculture and monitoring their dosages and frequencies are highly necessitated to avoid their adverse effect on the aquaculture environment.

Adsorbent selection for pesticides removal from drinking water

Pesticides present in water resources can cause adverse health effects even in low concentrations, due to their bio-accumulative character. Therefore, the challenge for drinking water production increases, due to the limitations of conventional water treatment technologies in the removal of small molecular weight dissolved compounds. This work aimed to provide technical and scientific support for the selection of pulverized activated carbon - PACs, granular activated carbon - GACs, and carbon nanotubes - CNT concerning atrazine - ATZ, simazine - SMZ, and diuron - DIU adsorption for application in water treatment plants, considering two forms of application commercial product - CP and analytical standard - SD. These forms of application were tested aiming to verify the influence of the purity of the products used in experiments on the adsorption efficiency. It was possible to verify the adsorption efficiencies were not guided only by the characteristics of the adsorptive materials used, and that the selection should not be carried out only based on the, specific superficial area - BET size and distribution of specific pore volume. The isotherms demonstrated that the parameter Kf associated with the results of the selection experiment can be considered an alternative technical tool of simple application and sufficient for this purpose. Also, the capacity of activated carbons - ACs and nanomaterials - NMs were affected by the application of the compounds, highlighting the importance of using commercial product - CP in scientific research and technical investigations.Hightlights The pesticides efficiency removal was affected due to the forms of application, SD and CP;The parameters IN and MBI were not decisive in the selection of the activated carbon;The main adsorption mechanism in all the materials was chemical;GAC was the most efficient adsorbent in the removal of the pesticides;An adequate adsorbent selection is crucial for satisfactory removal of pesticides in water.

Isolation of 2 simazine-degrading bacteria and development of a microbial agent for bioremediation of simazine pollution

Simazine was one of the most commonly used herbicides and was widely used to control broadleaf weeds in agriculture and forestry. Its widespread use had caused wide public concern for its high ecological toxicity. In order to remove simazine residues, 2 strains capable of effectively degrading simazine were isolated from the soil and named SIMA-N5 and SIMA-N9. SIMA-N5 was identified as Bacillus licheniformis by 16SrRNA sequence analysis, and SIMA-N9 was Bacillus altitudinis. According to the degradation ratio of simazine in a certain period of time, the degradation ability of different strains was evaluated. The degradation efficiency of simazine (5 mg/L) by SIMA-N9 could reach about 98% in 5d, and the strain SIMA-N5 could reach 94% under the same conditions. In addition, the addition of Pennisetum rhizosphere soil during the process of degrading simazine by strain SIMA-N9 could effectively improve the degradation efficiency. The strain SIMA-N9 has been developed as a microbial agent for the bioremediation of simazine contamination in soil. The new microbial agent developed by using SIMA-N9 has achieved satisfactory application effects. Based on the research results already obtained in this study, it was considered that strain SIMA-N9 and its live bacterial agent could play an important role in bioremediation of simazine pollution. This study could not only provide a set of solutions to the simazine pollution, but also provide a reference for the treatment of other pesticide pollution.

Ecological risk assessment of pesticide residues in soils from vegetable production areas: A case study in S-Nepal

Pesticides pose a serious risk to ecosystems. In this study, we used European Food Safety Authority methods, such as risk quotient (RQ) and toxicity exposure ratios (TER), to assess the potential ecological risks of 15 pesticide residues detected in agricultural soils in the Gaidahawa Rural Municipality of Nepal. The mean and maximum concentrations of the detected pesticide residues in the soil were used for risk characterization related to soil organisms. RQ_mean, TER_mean and RQ_maximum, TER_maximum were used to determine general and the worst-case scenarios, respectively. Of all the detected pesticides in soils, the no observed effect concentration (NOEC) for 27% of the pesticides was not available in literature for the tested soil organisms and their TER and RQ could not be calculated. RQ threshold value of ≥1 indicates high risk for organisms. Similarly, TER threshold value of ≥5, which is acceptable trigger point value for chronic exposure, indicates an acceptable risk. The results showed that the worst-case scenario (RQ_maximum) indicated a high risk for soil organisms from chlorpyrifos [RQ_maximum > 9 at depths (cm) of 0-5, 15-20 and 35-40 soil layer]; imidacloprid (1.78 in the 35-40 cm soil layer) and profenofos (3.37 in the 0-5 cm and 1.09 in the 35-40 cm soil layer). Likewise, for all the soil depths, the calculated TER for both the general and worst-case scenarios for chlorpyrifos ranged from 0.37 to 3.22, indicating chronic toxicity to F. candida. Furthermore, the risk of organophosphate pesticides for soil organisms in the sampling sites was mainly due to chlorpyrifos, except for two study sites where the risk was from profenofos. Ecological risk assessment (EcoRA) of the pesticide use in the study area indicated that the EFSA soil organisms were at risk at some of the localities where farmers practiced conventional farming.

Bioassays to assess the ecotoxicological impact of polyethylene microplastics and two organic pollutants, simazine and ibuprofen

Research on the environmental impact of plastics, especially on the effect of microplastics (MPs), has become a priority issue in recent years, mainly in terrestrial ecosystems where there is a lack of studies. This work aims to assess the impact of two types of polyethylene MPs, white microbeads (W) and fluorescent blue microbeads (FB), and their interactions with two contaminants, ibuprofen (Ib) and simazine (Sz), on different organisms. A set of bioassays for Vibrio fischeri, Caenorhabditis elegans and Lactuca sativa was carried out, which helped to establish the ecotoxicological impact of those pollutants. C. elegans showed the least sensitivity, while V. fischeri and L. sativa showed a high toxicological response to MPs alone. We found that W and FB induced an inhibition of 27% and 5.79%, respectively, in V. fischeri, and the growth inhibition rates were near 70% in L. sativa for both MPs. MPs exhibited a potential role as contaminant vectors in V. fischeri since the inhibition caused by W-Ib or W-Sz complexes was near 39%. The W-Sz complex significantly reduced leaf development in L. sativa, and a reduction of 30% in seed germination was detected when the complex FB-Sz was tested. This study reveals the importance of designing a complete set of analyses with organisms from different trophic levels, considering the great variability in the effects of MPs and the high number of relevant factors.

The profiling of elements and pesticides in surface water in Nanjing, China with global comparisons

The study on high-throughput determination covering various kinds of elements and pesticides in surface water is rarely reported. The surface water samples were collected from the Yangtze River, the Qinhuai River and the Xuanwu Lake in Nanjing which is a large and populous city in eastern China, and elementome (47 elements) and pesticide exposome (60 pesticides) were profiled, which were characterized by univariate and multivariate statistical analysis, literature comparison, and risk assessment. A total of 47 elements and 47 pesticides were detectable. By combining the results of univariate and multivariate statistical analysis, we consistently found that the levels of elements in the Qinhuai River were relatively higher than those in the Yangtze River and the Xuanwu Lake, mainly including rare earth elements and macroelements. The concentrations of isoprocarb, profenofos and simazine in the Yangtze River were relatively higher than those in the Qinhuai River and the Xuanwu Lake. Based on literature search and our data, the results about global element and pesticide concentrations in surface water were summarized. The surface water in Nanjing showed notably higher aluminum level when compared to the level around the world. The risk assessment suggested that arsenic posed a considerable carcinogenic risk. This study provided a large volume of first-hand information about the profiles of elements and pesticides in surface water, which can be used for warning of surface water pollution and preventing potential hazardous effect on public health.

Effects of NaOH Activation on Adsorptive Removal of Herbicides by Biochars Prepared from Ground Coffee Residues

In this study, the adsorption of herbicides using ground coffee residue biochars without (GCRB) and with NaOH activation (GCRB-N) was compared to provide deeper insights into their adsorption behaviors and mechanisms. The physicochemical characteristics of GCRB and GCRB-N were analyzed using Brunauer–Emmett–Teller surface area, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction and the effects of pH, temperature, ionic strength, and humic acids on the adsorption of herbicides were identified. Moreover, the adsorption kinetics and isotherms were studied. The specific surface area and total pore volume of GCRB-N (405.33 m2/g and 0.293 cm3/g) were greater than those of GCRB (3.83 m2/g and 0.014 cm3/g). The GCBR-N could more effectively remove the herbicides (Qe,exp of Alachlor = 122.71 μmol/g, Qe,exp of Diuron = 166.42 μmol/g, and Qe,exp of Simazine = 99.16 μmol/g) than GCRB (Qe,exp of Alachlor = 11.74 μmol/g, Qe,exp of Diuron = 9.95 μmol/g, and Qe,exp of Simazine = 6.53 μmol/g). These results suggested that chemical activation with NaOH might be a promising option to make the GCRB more practical and effective for removing herbicides in the aqueous solutions.

Activated Carbon and Ozone to Reduce Simazine in Water

In this study, the reduction of the pesticide simazine at an initial concentration of 0.7 mg L−1 in water has been investigated using two different technologies: adsorption with powdered and granulated activated carbon, advanced oxidation processes with ozone and finally, the combination of both technologies. The results obtained for a carbon dose of 16 mg L−1 show that powdered activated carbon, with contact times of 60 min, obtained 81% of reduction and in 24 h 92%, while granulated activated carbon at 60 min obtained a reduction of 2%, rising to 34% after 24 h of contact time. Therefore, powdered activated carbon achieves better reductions compared to granulated; when ozone was applied at a dose of 19.7 mg L−1, with a reaction time of 18 min, a reduction of 93% was obtained, achieving a better reduction in less time than with adsorption treatments; however, during oxidation, by-products of simazine were produced. In the combined treatments, with the same doses of carbon and ozone mentioned above, the treatment that starts with ozone followed by activated carbon powder is recommended due to the adsorption in the last phase reaching a 90% reduction of the simazine and its by-products in 38 min of time.

History traces of HCHs and DDTs by groundwater dating and their behaviours and ecological risk in northeast China

Organochlorine pesticides legacies, such as hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT), remained in sediments or soils due to their difficulty in decomposition, especially in the agricultural areas where pesticides were widely used historically. Different from the little disturbed depositional environment of lake, it was difficult for rivers to explore the timing of DDT and HCH inputs through dating sediment cores as records. Based on groundwater dating, this study ascertained the historic pollution of DDT and HCH in Taizi River basin. HCH and DDT residues in groundwater were consistent with the historical production and usage, which increased from the 1950s to the 1980s and declined from the 1980s to the 1990s. Moreover, the partitioning behaviours of HCHs and DDTs in surface water and suspended particulate matter were discussed. It was revealed that β-HCH and o,p'-DDT were more likely to attach to suspended particulate matter than other isomers. Furthermore, species sensitivity distribution curves were generated using 54 toxicity data records to assess the risk of HCHs and DDTs in water and suspended particulate matter. These results indicated that p,p'-DDT in surface water posed a high risk to 95% of the aquatic life in the long run.

Bead-immobilized Pseudomonas stutzeri Y2 prolongs functions to degrade s-triazine herbicides in industrial wastewater and maize fields

Functional durability of bio-augmented microbes in contaminated fields remains a major challenge in bioremediation. In the present study, various immobilization materials and compositional combinations were designed and compared to enhance the functional durability of Pseudomonas stutzeri sp. Y2 for degradation of simazine, one of the most used herbicides, in industrial wastewater and maize fields. Among four combinations of materials tested, the optimal combination obtained from the orthogonal array trials was 14% polyvinyl alcohol (PVA), 1-3% sodium alginate (SA), 2% activated carbon (AC), and 1-2% Y2 cells (PSC-Y2), which yielded 1.7 fold faster degradation of simazine at 50 mg L^-1 than that by free Y2 cells in the industrial wastewater. The degradation half-lives (DT₅₀) of simazine (10 mg L^-1) by free Y2 cells and PSC-Y2 was 1.1 d and 5.3 d in laboratory soil, respectively. The DT₅₀ of simazine by PSC-Y2 at the recommended and double dosages of simazine (0.45 and 0.9 g ai·m^-2) was 17.2 d and 12.4 d in the maize fields, respectively, in comparison with 23 d and 17.4 d by free Y2 cells. In addition, the PSC-Y2 degraded 100% of atrazine and terbuthylazine, and 96% of propazine at an initial concentration of 50 mg L^-1 each in 4 days. This study provides an immobilization strategy to stabilize bacteria and prolong bacterial functions to treat s-triazine herbicides contaminated water and soil.

Pesticides and herbicides

This paper provides a review of some important scientific articles published in the year 2018 about pesticides and herbicides. The literature review presented in this paper cover pesticides and herbicides presence as well as occurrence in the environment. The review is divided into four sections. Each of these sections highlight issues related to pesticides and herbicides on toxicology, ecology, risk assessment, modeling, and treatment strategies.