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Rice straw incorporation is globally recognized as a viable alternative to incineration. However, it might lead to arsenic (As) methylation in soils, resulting in increased accumulation of methylated As in rice plants, potentially contributing to the emergence of rice straighthead disease. To evaluate the effect of straw incorporation on the As transformation in the paddy field system, we conducted a pot experiment for rice cultivation in two paddy soils with different As background levels and also characterized the response of the soil microbial community to straw incorporation. The results showed that straw incorporation elevated the total and methylated As concentration within the soil solution and rice plants, which in turn reduced rice seed setting rate and yield, and caused straighthead disorder in rice cultivated in soils with high As levels. 16S rRNA-based sequencing demonstrated reduced abundance and diversity of microorganisms upon adding straw. Notably, the dominant phylum, Bacteroidetes, exhibited a significant increase in abundance due to straw integration, while the abundance of Proteobacteria and Acidobacteria decreased. At the family level, the prevalence of Rikenellaceae increased only in soils contaminated with As following straw incorporation. Redundancy analysis showed positive associations between Rikenellaceae and levels of methylated As present in both soil porewater and rice husks, suggesting a potentially pivotal role of Rikenellaceae in the As methylation process after straw integration. These findings collectively emphasize that including straw can reshape the soil's microbial community and amplify As methylation in the soil, thereby promoting the uptake and accumulation of methylated As in rice and inducing straighthead disease in As-contaminated soil., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Rice (Oryza sativa L.) is one of the most important staple food crops worldwide. For people fed on rice, toxic elements cadmium (Cd) and arsenic (As) and mineral nutrients in rice are pivotal to evaluate potential risks of harmful element intake and malnutrition. We collected rice samples of 208 cultivars (83 inbred and 125 hybrid) from fields in South China and determined Cd, As, As species, and mineral elements in brown rice. Chemical analysis shows that the average content of Cd and As in brown rice were 0.26 ± 0.32 and 0.21 ± 0.08 mg·kg -1 , respectively. Inorganic As (iAs) was the dominative As species in rice. Rice Cd and iAs in 35.1% and 52.4% of the 208 cultivars exceeded rice Cd and iAs limits, respectively. Significant variations of rice subspecies and regions were found for Cd, As, and mineral nutrients in rice (P < 0.05). Inbred rice had lower As uptake and more balanced mineral nutrition than hybrid species. Significant correlation was observed between Cd, As versus mineral elements like Ca, Zn, B, and Mo (P < 0.05). Health risk assessment indicates that high risks of non-carcinogenic and carcinogenic of Cd and iAs, and malnutrition, in particular Ca, protein and Fe deficiencies, might be caused by rice consumption in South China., (© 2023. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Roxarsone (ROX), an organoarsenic feed additive, and its metabolites, can be present in animal manure used to fertilize rice. Rice is prone to absorb arsenic, and is subject to straighthead disorder, which reduces rice yield and is linked with organic arsenic compounds. This study aims to elucidate how soil property affect arsenic accumulation in rice plants fertilized with chicken manure containing ROX metabolites. Manures of chickens fed without or with ROX, designated as control manure and ROX treated manure (ROXCM), respectively, were applied in eight paddy soils of different origins, to investigate the assimilation of arsenic species in rice plants. The results show that inorganic arsenic (arsenate and arsenite), monomethylarsonic acid and dimethylarsinic acid (DMA) were detected in all brown rice and husk, trace tetramethylarsonium and trimethylarsine oxide were occasionally found in these both parts, whereas all these arsenic species were determined in straw, irrespective of manure type. ROXCM application specifically and significantly increased brown rice DMA (P = 0.002), which remarkably enhanced the risk of straighthead disease in rice. Although soil total As impacted grain biomass, soil free-iron oxides and pH dominated arsenic accumulation by rice plants. The significantly increased grain DMA suggests manure bearing ROX metabolites is not suitable to be used in soils with abundant free-iron oxides and/or high pH, if straighthead disorder is to be avoided in rice., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Roxarsone (ROX), an organoarsenic feed additive, occurs as itself and its metabolites including As(V), As(III), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in animal manure. Animal manure improves soil biological property, whereas As compounds impact microorganisms. The integral influence of animal manure bearing ROX metabolites on soil biological quality is not clear yet. Herein, the effect of four chicken manures excreted by chickens fed with four diets containing 0, 40, 80 and 120 mg ROX kg -1 , on soil biological attributes. ROX addition in chicken diets increased total As and ROX metabolites in manures, but decreased manure total N, ammonium and nitrate. The elevated ROX metabolites in manures increased soil total As, As species and total N, and increased first and then decreased soil nitrate and nitrite, but did not affect soil ammonium in manure-applied soils. The promoting role of both soil As(III) and ammonium on soil microbial biomass carbon and nitrogen, respiration and saccharase activity, were exceeded or balanced by the inhibiting effect of soil nitrate. The suppression of soil catalase activity by soil As(V) was surpassed by the enhancement caused by soil nitrate and nitrite. Soil urease, acid phosphatase and polyphenol oxidase activities were not suitable bioindicators in the four manure-amended soils. Soil DMA did not affect soil biological properties, and MMA was not detectable in all manure-amended soils. The above highlights the complexity of joint influence of soil As and N on biological attributes. Totally, when ROX is used at allowable dose in chicken diet, soil biological quality would be suppressed in manure-amended soil., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The environmental and human health risk posed by veterinary antibiotics is of global concern. Antibiotic uptake by herbal plants has been studied, but little is known about perennial woody fruit crops. Litchi (Litchi chinensis Sonn.), a longevial fruit tree, is routinely fertilized with animal manure and, therefore, may be at risk of antibiotic uptake into its fruits. This study investigated the degradation of chlortetracycline and doxycycline present in manure used to amend orchard soil, and their subsequent assimilation by litchi plant, as affected by manure application rate. The results show that half-lives of chlortetracycline and doxycycline in soil were decreased by increased manure rate, with an average of 27 and 59 days, respectively. Chlortetracycline was readily transported to litchi shoots and increased with the growth of litchi plants. Doxycycline predominantly remained in the roots, and underwent growth dilution in the plants. The two tetracyclines could not be detected in fruits from litchi trees when applied with manures, at various rates, over 2 years. For litchi, chlortetracycline may pose human health risk through manure application, but doxycycline is unlikely to do so. Long-term field experiments are required to monitor antibiotic accumulation in fruits of perennial fruit trees fertilized with animal manure.

Roxarsone (ROX), a widely used feed organoarsenic additive, occurs as itself and its metabolites in animal manure that is commonly land used as fertilizer. Soil property impacts arsenic (As) speciation and bioavailability. Fourteen soils across China were used to conduct culture experiments to investigate As uptake by garland chrysanthemum (ChrysanthemumL coronarium), with the soils fertilized with chicken manure bearing ROX and its metabolites. The results show As(III) was the sole As form in garland chrysanthemum shoots, and As(III) and As(V) occurred in roots. Only inorganic As was detected in all soils when the plants were harvested. Stepwise regression analysis shows soil-exchangeable Ca predominated shoot As(III) concentration (shoot As(III) = 1.60030 soil Ca, R 2  = 0.8832***). Therefore, ROX is transferred into the human food chain finally as inorganic As in plants. Application of animal manure bearing ROX and its metabolites is not recommended in Ca-rich soils to avoid excess inorganic As dietary exposure.

Roxarsone (ROX), a widely used feed additive, occurs as itself and its metabolites in animal manure. Rice is prone to accumulate As than other staple food. Four diets with 0, 40, 80 and 120mgROXkg(-1) were fed in chickens, and four chicken manures (CMs) were collected to fertilize rice plants in a soil culture experiment. Linear regression analysis shows that the slopes of As species including 4-hydroxy-phenylarsonic acid, As(V), As(III), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in CM versus dietary ROX were 0.033, 0.314, 0.033, 0.054 and 0.138, respectively. Both As(III) and DMA were determined in all rice grains, and As(III), As(V), MMA and DMA in rice hull, but detectable As forms in rice straws and soils increased with increasing ROX dose. Grain As(III) was unrelated to ROX dose but exceeded the Chinese rice As limit (0.15mgAs(III)kg(-1)). Dietary ROX enhanced straw As(III) mostly, with the slope of 0.020, followed by hull DMA (0.006) and grain DMA (0.002). The slopes of soil As(V) and As(III) were 0.003 and 0.001. This is the first report illustrating the quantitative delivery of ROX via food chain, which helps to evaluate health and environmental risks caused by ROX use in animal production., (Copyright © 2016 Elsevier B.V. All rights reserved.)