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

Effective degradation of atrazine by spinach-derived biochar via persulfate activation system: Process optimization, mechanism, degradation pathway and application in real wastewater

Herein, biochar derived from spinach remnants was prepared for the first-time for the utilization in persulfate (PS) activation to effectively degrade atrazine. Characteristics of the prepared biochar were explored using advanced analyses. Control experiments implied the efficient activation of PS in the presence of the synthesized biochar. The highest degradation of atrazine (99.8%) could be attained at atrazine concentration of 7.2 mg/L, PS concentration of 7.7 mM, biochar dose of 1.88 g/L and reaction time of 120 min. The prepared biochar displayed a high recyclability performance attaining degradation ratios of 98.2, 96.53, 96.4, 92.8 and 88% in five sequential cycles under the optimum conditions. The degradation mechanism was explored showing that sulfate radicals were the prime reactive species in the degradation system. The degradation intermediates were specified, and the degradation pathways were propositioned. The highest REs in agrochemical industrial wastewater reached 80.21 and 83.43% of atrazine and TOC after 2 h. NH₃ (348.4 mg/L) was reduced to 168.3 mg/L (RE: 51.7%) while level of NO₃ (94.7 mg/L) was increased by 98.8% (188.3 mg/L) in the treated effluent due to oxidation of NH₃ to nitrite and then nitrate. Extension of reaction time could contribute to achieving full mineralization of the real wastewater due to the residual PS after 120 min. The effectiveness and low-cost of biochar@PS system as well as its high performance in degrading real wastewater support the efficiency of the prepared biochar to be applied on an industrial scale.

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

A state-of-the-art review on modeling the biochar effect: Guidelines for beginners

Biochar has been widely advocated due to its special properties and sustainability for agriculture soil amendment. The influencing mechanism of biochar on soil properties is a key aspect of quantifying and predicting its benefits and trade-offs. The contribution of biochar to both environmental and agricultural benefits has been deeply discussed and extensively reviewed, but few reviews have focused on modeling biochar effects. An overview of recent advances in biochar modeling is illustrated and approaches classified in this paper. Applications of a machine learning model, a deterministic model, and a numerical model to biochar are categorized and summarized. A discussion of the advantages and disadvantages of each model and a comparison among them are also provided. Finally, this paper gives many suggestions on narrowing the knowledge gap to advance biochar modeling. Further study of biochar modeling in management planning and design and application of the model results in agricultural systems will help accelerate the expansion of biochar's application scale and encourage the efficient utilization of waste in agricultural systems.

The quality of soil organic matter, accessed by 13C solid state nuclear magnetic resonance, is just as important as its content concerning pesticide sorption

The global increase of food production has been achieved mainly through the intensive use of inputs such as pesticides. Once released to the soil, sorption (which could be represented by Freundlich solid-water distribution coefficients - K_F) and degradation are two governing processes that determine the distribution and persistence of pesticides in the environment. In spite of the huge dataset, the only apparent generalisation is the high correlation between K_F and soil organic matter (SOM) content. However, in this work no correlation was observed between K_F and organic C content (OC) and so the obtained K_OC (K_F normalised by OC) spread out in a wide range: 1100 to 11,400 mL g^-1 for abamectin; and 30-150 mL g^-1 for atrazine, both ranges corroborate with data from literature. These high variabilities indicate that other soil components or SOM quality strongly interfere in the pesticide sorption in addition to SOM content. Seeking to estimate the influence of SOM quality in the abamectin and atrazine K_OC values, the humic acids, a fraction of the SOM, was analysed by ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) and Principal Component (PC) Regression. The first PC of ¹³C NMR spectra presented negative loadings for aliphatic compounds and positive loadings for aryl C, typical of partially oxidised pyrogenic C. Their scores showed strong correlation with the abamectin K_OC values (R² = 0.91, p < 5 10^-8) and weaker with atrazine K_OC (R² = 0.63, p < 0.0001), in addition to a smaller standardised slope: 1.01 for abamectin and 0.76 for atrazine. These results could be explained by the higher hydrophobicity of abamectin, being thus more prone to interact with the polycondensed aryl groups from the pyrogenic C. It is also important to highlight that humic acids are useful proxies for understanding the paramount interaction of SOM with pesticides.

A non-edible waste as a potential sorptive media for removal of herbicide from the watershed

A non-edible waste, from biodiesel processing industry is being turned to carbonaceous material (biochar) using slow pyrolysis. The material was found to be amorphous with hydroxyl, methyl, carbonyl and carboxyl functional groups onto the surface. The influencing parameters, namely adsorbate concentration (0.05-5 mg/l), biochar loading (0.02-0.4 g), pH(3-12) and particle sizes (0.03-0.13 mm) were studied to observe the effect on the sorption of simazine using biochar. A multivariate optimization using central composite design in response surface methodology was performed employing desirability function. The optimized biosorption efficiency (B%) and capacity q_e was found to be 91.98 % and 0.83 mg/g respectively with the optimized parameters as 3.76 mg/l of adsorbate concentration, 0.12 g of biochar loading, pH of 5.26 and 0.0535 mm of particle size. The simazine adsorption phenomena were found to be multilayer heterogeneous sorption based on Langmuir and Freundlich models. The kinetics investigation shows that chemisorption was involved for the transfer of simazaine to the surface of biochar with three distinct intra particulate diffusional zones. An adsorption process requires activation energy of 11.27 kJ/mol and the negative magnitude of  ΔH^* indicates the exothermicity involved in the process.

Removal of atrazine by biochar-supported zero-valent iron catalyzed persulfate oxidation: Reactivity, radical production and transformation pathway

Atrazine is a widely used herbicide whose presence poses a potential threat to agriculture and human living environment. This work studied the degradation performances and mechanisms of zero-valent iron and biochar composite (ZVI/BC) activated persulfate (PS) for atrazine. The results showed that the removal percentage of atrazine reached 73.47% within 30 min. Furthermore, the optimal parameters (175 mg/L ZVI/BC, 2 mM PS and initial pH of 3) were obtained through response surface methodology. Meanwhile, the high atrazine removal percentage (83.77%) was obtained under the optimal conditions. Radical quenching studies and electron spin resonance revealed that active substances produced during PS activation, as well as that SO₄·^- and HO· were dominant active species for the atrazine degradation. According to iron corrosion products and XPS analysis, the reaction mechanism of ZVI/BC-PS system was proposed as that ZVI loaded on the composites further activated PS to produce SO₄·^- and HO· which accompany with the valent changing of iron and finally causing degradation of atrazine. In addition, the degradation pathways of atrazine in ZVI/BC-PS system included dealkylation, alkyl oxidation and dechlorination-hydroxylation by the results of GC-MS and LC-MS. These findings demonstrated that ZVI/BC activated persulfate may be an efficient technique for the degradation of atrazine.

Mechanism of Cr(VI) removal by magnetic greigite/biochar composites

This study synthesized magnetic greigite/biochar composites (MGBs) by a solvothermal method and tested their ability to remove Cr(VI) from heavy metal-polluted wastewater. X-ray diffraction (XRD), Fourier transformed infrared spectrometry (FT-IR) and scanning electron microscopy (SEM) revealed that magnetic greigite (Fe₃S₄) flakes were aggregated and anchored to the biochar surface, resulting in more active sites than pristine biochar. Maximum Cr removal efficiency and capacity of MGB-30 (greigite/biochar = 30%) at an initial Cr(VI) concentration of 20 mg/L were 93% and 23.25 mg/g, respectively. A pseudo-first-order kinetic model was determined for the Cr(VI) removal process and the Cr(VI) removal rate constants were highly dependent on the mass ratios of Fe₃S₄ loaded on biochar, initial MGB and Cr(VI) concentrations and solution pH. X-ray photoelectron spectroscopy (XPS) and flame atomic absorption spectrometric (FAAS) analysis demonstrated that Cr(VI) was preferentially adsorbed on MGBs and subsequently reduced to Cr(III) by MGBs. Electron paramagnetic resonance (EPR) spectroscopy and iron redox transformations revealed that the Cr(VI) removal enhancement was attributed to efficient surface Fe(III)/Fe(II) cycling via electron transfer with the persistent free radicals (PFRs) of biochar. These novel findings provide new insights into the Fe(III)/Fe(II) cycle induced by biochar and the prospects of using magnetic greigite/biochar composites for remediation of Cr(VI)-rich wastewaters.

The dissipation of cyazofamid and its main metabolite in soil response oppositely to biochar application

Biochars derived from rice straw (RS), corn straw (CS), chicken manure (CM) and tire rubber (TR) were applied to soil to investigate their effects on the dissipation of cyazofamid and its metabolite CCIM (4-chloro-5-p-tolylimidazole-2-carbonitrile), with high acute toxicity compared to cyazofamid. The enhancement of cyazofamid dissipation followed the order of CS > RS > CM, whereas TR depressed the cyazofamid dissipation. Adsorption, hydrolysis and microbial degradation were all involved in cyazofamid dissipation. CM and CS enhanced the contribution of biodegradation to cyazofamid dissipation, which might be related with the shifted microbial community. More importantly, CCIM residual was drastically increased by 8-15 times after biochar application, regardless of biochar type. In total, this study shed light on the issue of build-up of metabolites in biochar-amended soil, especially for metabolites having higher toxicities than parent compounds, providing new insights into potential risk of biochar application for soil remediation.

Nanosorbent of hydroxyapatite for atrazine: A new approach for combating agricultural runoffs

The attention of current work was on the fabrication of effective nanoadsorbent of hydroxyapatite (HAp) for the controlled release of atrazine (ATZ) formulation. The ATZ-HAp complex (ATZ@HAp) was able to inhibit the growth of Brassica sp. under in situ conditions. This developed methodology aspires to cease the agricultural runoffs of ATZ applied with the HAp adjuvant and ensure their effective functioning. The efficacy of the protocol was mainly accomplished by adsorbing ATZ over the surface of HAp NPs that restricted its premature runoff and promoted the prolonged herbicidal efficiency. The influence of fundamental parameters i.e., HAp dose, ATZ dose and initial pH on the adsorption process was investigated systematically. The suitability of ATZ@HAp complex for real world application was adjudged after proofing its toxicological behaviour and its role in Zea mays plantations. The complex was found to be non-toxic and nurturing due to its phosphate rich nature. Further investigations of ATZ@HAp complex and its effect on the non-target species will help in establishing an effective framework for their commercial use in agricultural practices.

Quantitative evaluation of relationships between adsorption and partition of atrazine in biochar-amended soils with biochar characteristics

Atrazine (ATZ) adsorption in two natural soils amended with biochars produced from different feedstocks at 300, 500, and 700 °C were investigated; further, the relationships between the surface and partition adsorption capacities of ATZ in biochar-amended soils with biochar characteristics were quantitatively evaluated. The results revealed that high aromaticity, hydrophobicity, and low polarity of biochar facilitated ATZ adsorption. The addition of selected biochars significantly increased the adsorption of ATZ on paddy soil (PS) and black soil (BS) by 5.2–7.5 times and 2.3–4.2 times, respectively. On the contrary, the degree of increase in surface adsorption was much higher than that in partition adsorption, mainly due to the role of the specific adsorption of ATZ on biochar. Meanwhile, the respective contributions of surface and partition adsorptions to the total ATZ adsorption on biochar-amended soil changed with different addition amounts of biochar. The multiple nonlinear regression analysis demonstrated the linear dependence of H/C ratio, (O + N)/C ratio, and specific surface area (SSA) of biochar on the surface adsorption capacity of biochar-amended PS and BS, as well as the linear dependence of organic carbon and ash contents on the partition adsorption capacity of biochar-amended PS and the linear dependence of the H/C ratio and SSA on the partition adsorption capacity of biochar-amended BS. In biochar-amended soil systems, interactions between biochar and soil could affect ATZ adsorption, and organic matter in biochar might compensate for the role of soil organic matter in the competition for adsorption sites with a decrease in the biochar pyrolysis temperature.

Adsorption of atrazine (ATZ) in two natural soils amended with different biochars was investigated, and the relationships of adsorption capacity of biochar-amended soils with biochar characteristics were also quantitatively evaluated.

Fabrication and characterization of hydrophilic corn stalk biochar-supported nanoscale zero-valent iron composites for efficient metal removal

Pyrolyzing low-cost agro-waste into biochar is a promising means for waste biomass utilization. This study engineers corn stalk-derived biochar with abundant hydrophilic functional groups as a support material for iron nanoparticles impregnation (nZVI-HCS). Surface chemistry and morphology of nZVI-HCS composites is characterized by SEM, TEM, TG, XRD, FTIR, XPS, and BET techniques, which helps to elucidate the mechanisms of Pb²⁺, Cu²⁺ and Zn²⁺ removal from single and mixed-metal solutions in batch experiments. Equilibrium adsorption capacities can reach 195.1, 161.9 and 109.7 mg·g^-1 for Pb²⁺, Cu²⁺ and Zn²⁺ at neutral medium after 6-h process, respectively. The engineered biochar with hierarchical pores can impregnate iron nanoparticles, serve as an adsorbent, and enhance metal reduction/precipitation. Rapid removal and high performance can be maintained after five regeneration/reuse cycles. Multiple interaction mechanisms including adsorption, precipitation, reduction and complexation are responsible for metal removal by nZVI-HCS composites, which can be a novel biowaste-derived material for wastewater treatment.

Effects of environmentally relevant sub-chronic atrazine concentrations on African clawed frog (Xenopus laevis) survival, growth and male gonad development

Sub-chronic toxicity of environmentally relevant atrazine concentrations on exposed tadpoles and adult male African clawed frogs (Xenopus laevis) was evaluated in a quality controlled laboratory for 90 days. The aim of this study was to determine the effects of atrazine on the survival, growth and gonad development of African clawed frogs. After exposure of tadpoles to atrazine concentrations of 0 (control), 0.01, 200 and 500 μg L^-1 in water, mortality rates of 0, 0, 3.3 and 70% respectively were recorded for the 90 day exposure period. Morphometry showed significantly reduced tadpole mass in the 500 μg L^-1 atrazine exposed tadpoles (p < 0.05). Light microscopy on testes of adult frogs exposed to the same atrazine concentrations using hematoxylin and eosin (H&E) and Van Gieson staining techniques revealed gonadal atrophy, disruption of germ cell lines, seminiferous tubule structure damage and formation of extensive connective tissue around seminiferous tubules of frogs exposed to 200 μg L^-1 and 500 μg L^-1 atrazine concentrations. Ultrastructural analysis of the cellular organelles using transmission electron microscopy (TEM) revealed significant amounts of damaged mitochondria in testosterone producing Leydig cells as well as Sertoli cells. Biochemical analysis revealed reduced serum testosterone levels in adult frogs at all exposure levels as well as presence of six atrazine metabolites in frog serum and liver. The results indicate that atrazine concentrations greater than the calculated LC50 of 343.7 μg L^-1 cause significant mortality in tadpoles, while concentrations ≥200 μg L^-1 adversely affect reproductive health of adult frogs and development of tadpoles sub-chronically exposed to atrazine.

A novel method for synthesis of polyaniline and its application for catalytic degradation of atrazine in a Fenton-like system

Recently, polyaniline (PANI) has received widespread attention for the free volume, optical transmittance and electrical conductivity. In this study, a chemical vapor deposition method was developed to synthesize the conductive PANI-clay composite catalyzed by Fe(III)-saturated attapulgite (Fe(III)-ATTP). The reaction is initiated by the electron transfer from aniline (ANI) to Fe(III), subsequently generating ANI radical cation. The radical could further polymerize and form PANI in the constrained micropore structure of ATTP. The Raman, Fourier transform infrared and X-ray photoelectron spectra confirmed the formation of PANI on Fe(III)-ATTP surface by comparison with the PANI standard. The newly synthesized Fe(III)-ATTP-PANI composite exhibited superior reactivity as indicated by the efficient dissipation of atrazine in the presence of hydrogen peroxide (H₂O₂), and the degradation rate increased up to almost 150 times compared to Fe(III)-ATTP. The higher reactivity of Fe(III)-ATTP-PANI/H₂O₂ system was attributed to the accelerated electron transfer, the formation of ferrous ions, and the enhanced adsorption of atrazine onto attapulgite. Furthermore, our experimental results demonstrated that Fe(III)-ATTP-PANI showed good stability and it could be reused for several reaction cycles with high reactivity. This new material could act as an environmental-friendly catalyst in Fenton-like reaction system and show promising potential to effectively eliminate many persistent organic contaminants.

Characterization of modified biochars prepared at low pyrolysis temperature as an efficient adsorbent for atrazine removal

In this study, biochars (BC, ZnBC, and PBC) produced from wheat straw at relatively lower pyrolysis are successfully fabricated using different pretreatment techniques (without and with ZnCl₂ or H₃PO₄). The specific surface area (SSA), elemental analysis, and Fourier transform infrared spectra (FTIR) are used to analyze physicochemical properties of unmodified and modified biochars. ZnBC and PBC show higher specific surface area and more micropore structure than pure BC. Kinetic models (pseudo-first order, pseudo-second order, and intra-particle diffusion) as well as isotherm models (Langmuir and Freundlich) are applied to analyze adsorption behavior. Adsorption on biochars can be better fitted by the pseudo-second-order and intra-particle diffusion models, indicating that micropores and mesopores play important roles on adsorption process and chemisorption is dominant. The adsorption process is also affected by physical and chemical adsorption. In conclusion, biochar is a low-cost, effective, and environment-friendly adsorbent implicating in the environment for pesticide removal. Graphical abstract.