Heavy metal contamination in protected-field vegetable production has aroused widespread concern and manure is considered to be one of the contamination sources. Little is known about its long-term effects on heavy metal pollution in uncontaminated soils. A 15-year protected-field vegetable production experiment was carried out with three manure treatments (chicken manure: cattle manure = 3:1) with high (HMAR), medium (MMAR) and low (LMAR) application rates to evaluate the long-term risks of heavy metal pollution. It was found that continuous and high manure application rates significantly increased the total concentrations of soil Cd, Zn, Cr, and Cu rather than Pb, Ni or As. The high application rate of manure also increased soil available heavy metals although the soil organic matter was increased as well. Though total soil Cd under the HMAR exceeded the threshold of national soil standard, Cd content in tomato and fennel still complied with the food safety requirements of vegetables. Generally, the accumulation rates of soil Zn, Cu, and Cr with 1 t⋅ha⁻¹ of manure application in three treatments were ranked by HMAR < MMAR < LMAR. Based on the results of the ratio of heavy metal accumulation risk (RAR), Zn, Cu, and Cr under HMAR and Cd and Zn under MMAR would exceed their soil threshold values within 100 years and RAR could be a useful indicator for monitoring the long-term risk of soil heavy metal pollution. Recommended manure application rates to guarantee a 100-year period of clean production were 44, 74, and 63 t⋅ha⁻¹⋅yr⁻¹ for Zn, Cu, and Cr, respectively. Measurements should be taken to minimize the risk of heavy metals (Cd, Zn, Cr, and Cu) pollution sourced from manure to ensure food safety and ‘cleaner’ protected-field vegetable production.

Mobile genetic elements (MGEs) play critical roles in transferring antibiotic resistance genes (ARGs) among different microorganisms in the environment. This study aimed to explore the fate of MGEs during chicken manure (CM) and bovine manure (BM) composting to assess horizontal transfer risks of ARGs. The results showed that the removal efficiency of MGEs during CM composting was significantly higher than that during BM composting, because the potential host bacteria of MGEs were eliminated largely during CM composting. Meanwhile, these potential host bacterial communities are significantly influenced by pH, NH4+, NO3− and total N, which can be used to regulate host bacterial communities to remove MGEs during composting. Projection pursuit regression further confirmed that composting can effectively reduce the horizontal transfer risk of ARGs, especially for CM composting. These results identified the critical roles of host bacterial communities in MGEs removal during composting of different animal manures.

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX) is an arsenic-containing compound widely used as a feed additive in poultry industries. ROX excreted in chicken manure can be transformed by microbes to different arsenic species in the environment. To date, most of the studies on microbial transformation of ROX have focused on anaerobic microorganisms. Here, we isolated a pure cultured aerobic ROX-transforming bacterial strain, CZ-1, from an arsenic-contaminated paddy soil. On the basis of 16S rRNA gene sequence, strain CZ-1 was classified as a member of the genus Enterobacter. During ROX biotransformation by strain CZ-1, five metabolites including arsenate (As[V]), arsenite (As[III]), N-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA), 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA) and a novel sulfur-containing arsenic species (AsC₉H₁₃N₂O₆S) were detected and identified based on high-performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICP-MS), HPLC-ICP-MS/electrospray ionization mass spectrometry (ESI-MS) and HPLC-electrospray ionization hybrid quadrupole time-of-flight mass spectrometry (ESI-qTOF-MS) analyses. N-AHPAA and 3-AHPAA were the main products, and 3-AHPAA could also be transformed to N-AHPAA. Based on the results, we propose a novel ROX biotransformation pathway by Enterobacter. sp CZ-1, in which the nitro group of ROX is first reduced to amino group (3-AHPAA) and then acetylated to N-AHPAA.

Clay minerals are the most popular adsorbents/amendments for immobilizing heavy metals in contaminated soils, but the dissolved organic matter (DOM) in soil environment would potentially affect the adsorption/immobilization capacity of clay minerals for heavy metals. In this study, the effects of DOM derived from chicken manure (CM) on the adsorption of cadmium (Cd2+) on two clay minerals, bentonite and zeolite, were investigated. The equilibrium data for Cd2+ sorption in the absence or presence of CM-DOM could be well-fitted to the Langmuir equation (R2 > 0.97). The presence of CM-DOM in the aqueous solution was found to greatly reduce the adsorption capacity of both minerals for Cd2+, in particular zeolite, and the percentage decreases for Cd2+ sorption increased with increasing concentrations of Cd2+ as well as CM-DOM in aqueous solutions. The adsorption of CM-DOM on zeolite was greater than that on bentonite in the absence of Cd2+, however, a sharp increase was observed for CM-DOM sorption on bentonite with increasing Cd2+ concentrations but little change for that on zeolite, which can be attributed to the different ternary structures on mineral surface. The CM-DOM modified clay minerals were utilized to investigate the effect of mineral-adsorbed CM-DOM on Cd2+ sorption. The adsorbed form was found to inhibit Cd2+ sorption, and further calculation suggested it primarily responsible for the overall decrease in Cd2+ sorption on clay minerals in the presence of CM-DOM in aqueous solutions. An investigation for the mineral surface morphology suggested that the mineral-adsorbed CM-DOM decreased Cd2+ sorption on bentonite mainly through barrier effect, while in the case of zeolite, it was the combination of active sites occupation and barrier effect. These results can serve as a guide for evaluating the performance of clay minerals in immobilizing heavy metals when animal manure is present in contaminated soils.

Concentrated animal feeding operations around the globe generate large amounts of nitrous oxide (N2O) in the surrounding atmosphere. Liquid animal waste systems have received little attention with respect to N2O emissions. We hypothesized that the solution chemistry of animal waste aqueous suspensions would promote conditions that lead to N2O supersaturation at the liquid/air interface. The concentration of dissolved N2O in poultry litter (PL) aqueous suspensions at 25 °C was 0.36 μg N2O mL−1, at least an order of magnitude greater than that measured in water in equilibrium with ambient air, suggesting N2O supersaturation. There was a nonlinear increase in the N2O Henry constants of PL from 2810 atm/mole fraction at 35 °C to 17 300 atm/mole fraction at 41 °C. The extremely high N2O Henry constants were partially ascribed to N2O complexation with aromatic moieties. Complexed N2O structures were unstable at temperatures > 35 °C, supplying the headspace with additional free N2O concentrations. Temperature-dependent N2O supersaturation at the liquid/air interface of animal waste.

Additives are considered a promising approach to accelerate the composting process and alleviate the dissemination of pollutants to the environment. However, nearly all previous articles have focused on the impact of additive amounts on the reduction of HMs, which may not fully represent the main factor shaping HMs bioavailability status during composting. Simultaneously, previous reviews only explored the impacts, speciation, and toxicity mechanism of HMs during composting. Hence, a global-scale meta-analysis was conducted to investigate the response patterns of HMs bioavailability and compost parameters to different additives, composting duration, and composting factors (additive types, feedstock, bulking agents, and composting methods) by measuring the weighted mean values of the response ratio "[ln (RR)]" and size effect (%). The results revealed that additives significantly lessened HMs bioavailability by ≥ 40% in the final compost products than controls. The bioavailability decline rates were −40%, −60%, −57%, −55%, −42%, and −44% for Zn, Pb, Ni, Cu, Cr, and Cd. Simultaneously, additives significantly improved the total nitrogen (TN) (+16%), pH (+5%), and temperature (+5%), and decreased total organic carbon (TOC) (−17%), moisture content (MC) (−18%), and C/N ratio (−19%). Furthermore, we found that the prolongation of composting time significantly promoted the effect of additives on declining HMs bioavailability (p < 0.05). Nevertheless, increasing additive amounts revealed an insignificant impact on decreasing the HMs bioavailability (p > 0.05). Eventually, using zeolite as an additive, chicken manure as feedstock, sawdust as a bulking agent, and a reactor as composting method had the most significant reduction effect on HMs bioavailability (p < 0.05). The findings of this meta-analysis may contribute to the selection, modification, and application of additives and composting factors to manage the level of bioavailable HMs in the compost products.

Chlorpyrifos (CPF), as an organophosphate insecticide extensively used in the modern agricultural system, has been gradually banned in many countries due to its reported health risks to organisms, including humans. This study used simulated paddy field experiments and carbon-14 tracing to explore the possibility of reducing environmental risks of chlorpyrifos application through appropriate agronomic practice. Results showed ¹⁴C-CPF concentration in rice plants planted in the red soil (RS) was significantly higher than that in black soil (BS) and fluvo-aquic soil (FS). The application of biochar and chicken manure in RS reduced ¹⁴C-CPF accumulation in rice plants, and the content of ¹⁴C-CPF in rice grains decreased by 25% and 50%, respectively. Adding biochar to all three soils reduced the migration of ¹⁴C-CPF, especially in FS with the highest risk of ¹⁴C-CPF migration. The addition of chicken manure in FS reduced the migration of ¹⁴C-CPF and the total residual amount of ¹⁴C-CPF in the soil. In addition, chicken manure treatment increased the formation of ¹⁴C-bound residues (BRs) in soils and changed the distribution ¹⁴C-BRs in humus. The results indicated that the degree of environmental risks associated with the CPF application varies with soil types and could be reduced by introducing suitable exogenous organic matter into different soils, which is of great significance for guiding the scientific application of chlorpyrifos in agronomic practices.

Manure application increases the transfer risk of antibiotic resistance to farmland. Especially, its impact remains unclear when it occurs in arsenic (As)-contaminated paddy soils, which is considered as a global environmental problem. In this work, we investigated the fate of antibiotic resistance genes (ARGs) in As-antibiotic co-contaminated paddy soils under the application of manure from different sources (pig manure, cow dung, and chicken manure). Differences in the aliphatic carbon and electron-donating capacities of these dissolved organic matters (DOM) regulated the transformation of iron and As by both biotic and abiotic processes. The regulation by pig manure was stronger than that by cow dung and chicken manure. DOM regulation increased the abundance of As-related functional genes (arsC, arrA, aioA, and arsM) in the soil and accelerated the transformation of As speciation, the highest proportion of As(III) being 45%–61%. Meanwhile, the continuous selection pressure provided by the highly toxic As(III) increased the risk of ARGs and mobile genetic elements (MGEs) via horizontal gene transfer. As-resistant bacteria, including Bacillus, Geobacter, and Desulfitobacterium, were finally considered as potential host bacteria for ARGs and MGEs. In summary, this study clarified the synergistic mechanism of As-antibiotic on the fate of ARGs in co-contaminated paddy soils, and provided practical guidance for the proper application of organic fertilizers.

The rapid expansion of organic rice cultivation areas have been accompanied by increased application of organic fertilizers. The high prevalence of soil antibiotic resistance caused by organic fertilizer application poses a severe threat to the agricultural and soil ecosystems. To date, research efforts and understanding of the effects and mechanism of action of the various organic fertilizers on antibiotic resistance in paddy soils remain poorly investigated. Tetracycline resistance genes (TRGs, including tetB, tetC, tetL, tetZ, tetM, tetO, tetT, and tetX), class 1 integron-integrase gene (intI1) and bacterial communities were characterized using quantitative-PCR and Illumina MiSeq sequencing, in paddy soils exposed to inorganic fertilizer (NPK), animal-derived organic fertilizer (AOF, composted swine and/or chicken manure), plant-derived organic fertilizer (POF, rapeseed cake and/or astragalus) and commercial organic fertilizer (COF, composted of animal manure mix with crop residues) applications. Compared with NPK, AOF applications significantly increased the relative abundance of TRGs, which was predominantly expressed in the increase of the relative abundance of tetC, tetM, tetO, tetT, and tetX, while POF and COF had no significant effect on the relative abundance of TRGs. Principal coordinate analysis revealed that AOF and POF significantly altered bacterial communities in paddy soils relative to NPK, while COF had no significant change of bacterial communities. Variation partitioning analysis indicated that soil physicochemical properties were the decisive factors for the changes of TRGs in organic paddy fields. Furthermore, redundancy analysis and the Mantel test showed that TRG profiles in AOF applied paddy soils were strongly influenced by electrical conductivity (EC). Total nitrogen (TN) and organic matter (OM) affected the distribution of TRGs in COF and POF applied paddy soils through a different mechanism. This study provides insights into the impacts of different types of organic fertilizer on the profiles of TRGs in paddy soils.

Brazil is one of the major global poultry producers, and the organic waste generated by the chicken slaughterhouses can potentially be used as a biofertilizer in agriculture. This study was designed to test the hypothesis that continuous use of biofertilizer to the crops, substituting the use of mineral fertilizer promote C-offset for the soil and generate crop energy efficiency for the production system. Thus, the objectives of this study were to evaluate the effects of biofertilizer use alone or in combination with mineral fertilizer on soil organic carbon (SOC) stock, carbon dioxide (CO₂) mitigation, C-offset, crop energy efficiency and productivity, and alleviation of environmental pollution. The experiment was established in southern Brazil on a soil under 15 years of continuous no-till (NT). Experimental treatments were as follows: i) Control with no fertilizer application, ii) 100% use of industrial mineral fertilizer (Min-F); iii) 100% use of organic waste originated from poultry slaughterhouses and hereinafter designated biofertilizer (Bio-F), and iv) Mixed fertilizer equivalent to the use of 50% mineral fertilizer + 50% of biofertilizer (Mix-F). Effects of experimental treatments were assessed for the crop sequence based on bean (Phaseolus vulgaris), soybean (Glycine max) and corn (Zea mays) in the summer and wheat (Triticum aestivum) and black oat (Avena strigosaSchreb) in the winter composing two crops per year, as follow: bean/wheat-soybean/black oat-corn/wheat-soybean/black oat-corn/wheat-bean. The continuous use of Bio-F treatment significantly increased the index of crop energy efficiency. It was higher than that of control, and increased it by 25.4 Mg CO₂eq ha⁻¹ over that of Min-F treatment because of higher inputs of crop biomass-C into the system. Further, continuous use of Bio-F resulted in a significantly higher CO₂eq stock and offset than those for Min-F treatment. A positive relationship between the C-offset and the crop energy efficiency (R² = 0.71, p < 0.001) indicated that the increase of C-offset was associated with the increase of energy balance and the amount of SOC sequestered. The higher energy efficiency and C-offset by application of Bio-F indicated that the practice of crop bio fertilization with poultry slaughterhouse waste is a viable alternative for recycling and minimizing the environmental impacts.