Long-term application of organic fertilization causes the accumulation of antibiotic resistome in earthworm gut microbiota.

Antibiotic resistance genes (ARGs), prevalent across multiple environmental media, threaten human health worldwide and are considered emerging environmental contaminants. Earthworm gut, a niche for bacteria to survive, represents a potential reservoir for ARGs in soil. However, the compositions of ARGs in the earthworm gut microbiota remain elusive, especially under field conditions. In this study, we applied high-throughput quantitative PCR to profile the ARGs in the gut microbiota of earthworms after chronic exposure to fertilizers. To elucidate the factors that impact the ARGs composition, the bacterial community of gut microbiota, mobile genetic elements (MGEs), soil (nutrients, heavy metals, and antibiotics) and the properties of gut content (pH and nutrients) were analyzed. A total of 98 subtypes among 9 major types of ARGs, and 3 different MGEs were detected in the gut microbiota of earthworms. Organic fertilizer (sewage sludge and chicken manure) application significantly increased the diversity and abundance of ARGs. Of the 1123 identified operational taxonomic units (OTUs) at 97% similarity cutoff, most of them were assigned to Firmicutes (55.5%) and Proteobacteria (33.6%) in earthworm gut microbiota. Long-term organic fertilization slightly changed the microbiota composition, but did not impact the diversity. Partial redundancy analysis (pRDA) revealed that bacterial community, combined with environmental factors (soil and gut content properties) and MGEs, explained 72% of the variations of ARGs in the earthworm gut. Furthermore, the co-occurrence pattern between ARGs and MGEs indicated that horizontal gene transfer via MGEs may occur in the earthworm gut. These findings improve the current understanding of the dynamics of soil fauna-associated ARGs and the gut microbiota of earthworms may be an underappreciated hotspot for ARGs in the environment.

Long-term organic fertilization increased antibiotic resistome in phyllosphere of maize.

Phyllosphere contains various microorganisms that may harbor diverse antibiotic resistance genes (ARGs). However, we know little about the composition of antibiotic resistome and the factors influencing the diversity and abundance of ARGs in the phyllosphere. In this study, 16S rRNA gene amplicon sequencing and high-throughput quantitative PCR approaches were employed to investigate the effects of long-term (over 10 years) organic fertilization on the phyllosphere bacterial communities and antibiotic resistome. Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes dominated in the phyllosphere bacterial communities. Long-term application of sewage sludge and chicken manure altered the phyllosphere bacterial community composition, with a remarkable decrease in bacterial alpha-diversity. A total of 124 unique ARGs were detected in the phyllosphere. The application of sewage sludge and chicken manure significantly increased the abundance of ARGs, with a maximum 2638-fold enrichment. Variation partitioning analysis (VPA) together with network analysis indicated that the profile of ARGs is strongly correlated with bacterial community compositions. These results improve the knowledge about the diversity of plant-associated antibiotic resistome and factors influencing the profile of ARGs in the phyllosphere.

Dehydrocostus lactone suppresses cell growth and induces apoptosis in recombinant human papilloma virus­18 HaCaT cells via the PI3K/Akt signaling pathway.

Dehydrocostus lactone is considered to be the major cholagogic ingredient of the Costus genus of plants. It exhibits strong cholagogic effects, and also exerts antimicrobial and antineoplastic activity. The present study aimed to investigate the effects of dehydrocostus lactone on the cell growth and apoptosis of recombinant human papilloma virus (HPV)­18 HaCaT cells. The HPV­18 genome was transfected into HaCaT cells, which were subsequently used for analysis. The results demonstrated that dehydrocostus lactone reduced the cell proliferation and induced apoptosis of HPV­18 HaCaT cells, as determined by MTT and N­acetyl­Asp­Glu­Val­Asp p­nitroanilide assays, respectively. Furthermore, caspase­3/9 activity was determined using a caspase­3/9 activity kit and western blotting was performed to investigate the expression of certain proteins. The results demonstrated that caspase­3/9 activities, and the protein expression of Bcl­2­associated X and p53, in HPV­18 HaCaT cells were significantly increased, while cyclin D1 protein expression was suppressed by dehydrocostus lactone. Additionally, dehydrocostus lactone significantly upregulated the protein expression of phosphatase and tensin homolog and inhibited the phosphatidylinositol 3­kinase (PI3K)/Akt signaling pathway in HPV­18 HaCaT cells. Therefore, the results of the present study indicate that dehydrocostus lactone may suppress cell growth and induce apoptosis in recombinant HPV­18 HaCaT cells via the PI3K/Akt signaling pathway, and may be a represent a novel potential therapeutic agent for the treatment of condyloma acuminatum.

Long-Term Nickel Contamination Increases the Occurrence of Antibiotic Resistance Genes in Agricultural Soils.

Heavy metal contamination is assumed to be a selection pressure on antibiotic resistance, but to our knowledge, evidence of the heavy metal-induced changes of antibiotic resistance is lacking on a long-term basis. Using quantitative PCR array and Illumina sequencing, we investigated the changes of a wide spectrum of soil antibiotic resistance genes (ARGs) following 4-5 year nickel exposure (0-800 mg kg-1) in two long-term experimental sites. A total of 149 unique ARGs were detected, with multidrug and ß-lactam resistance as the most prevailing ARG types. The frequencies and abundance of ARGs tended to increase along the gradient of increasing nickel concentrations, with the highest values recorded in the treatments amended with 400 mg nickel kg-1 soil. The abundance of mobile genetic elements (MGEs) was significantly associated with ARGs, suggesting that nickel exposure might enhance the potential for horizontal transfer of ARGs. Network analysis demonstrated significant associations between ARGs and MGEs, with the integrase intI1 gene having the most frequent interactions with other co-occurring ARGs. The changes of ARGs were mainly driven by nickel bioavailability and MGEs as revealed by structural equation models. Taken together, long-term nickel exposure significantly increased the diversity, abundance, and horizontal transfer potential of soil ARGs.

Field-based evidence for copper contamination induced changes of antibiotic resistance in agricultural soils.

Bacterial resistance to antibiotics and heavy metals are frequently linked, suggesting that exposure to heavy metals might select for bacterial assemblages conferring resistance to antibiotics. However, there is a lack of clear evidence for the heavy metal-induced changes of antibiotic resistance in a long-term basis. Here, we used high-capacity quantitative PCR array to investigate the responses of a broad spectrum of antibiotic resistance genes (ARGs) to 4-5 year copper contamination (0-800 mg kg-1 ) in two contrasting agricultural soils. In total, 157 and 149 unique ARGs were detected in the red and fluvo-aquic soil, respectively, with multidrug and ß-lactam as the most dominant ARG types. The highest diversity and abundance of ARGs were observed in medium copper concentrations (100-200 mg kg-1 ) of the red soil and in high copper concentrations (400-800 mg kg-1 ) of the fluvo-aquic soil. The abundances of total ARGs and several ARG types had significantly positive correlations with mobile genetic elements (MGEs), suggesting mobility potential of ARGs in copper-contaminated soils. Network analysis revealed significant co-occurrence patterns between ARGs and microbial taxa, indicating strong associations between ARGs and bacterial communities. Structural equation models showed that the significant impacts of copper contamination on ARG patterns were mainly driven by changes in bacterial community compositions and MGEs. Our results provide field-based evidence that long-term Cu contamination significantly changed the diversity, abundance and mobility potential of environmental antibiotic resistance, and caution the un-perceived risk of the ARG dissemination in heavy metal polluted environments.

Copper pollution decreases the resistance of soil microbial community to subsequent dry-rewetting disturbance.

Dry-rewetting (DW) disturbance frequently occurs in soils due to rainfall and irrigation, and the frequency of DW cycles might exert significant influences on soil microbial communities and their mediated functions. However, how microorganisms respond to DW alternations in soils with a history of heavy metal pollution remains largely unknown. Here, soil laboratory microcosms were constructed to explore the impacts of ten DW cycles on the soil microbial communities in two contrasting soils (fluvo-aquic soil and red soil) under three copper concentrations (zero, medium and high). Results showed that the fluctuations of substrate induced respiration (SIR) decreased with repeated cycles of DW alternation. Furthermore, the resistance values of substrate induced respiration (RS-SIR) were highest in non-copper-stressed (zero) soils. Structural equation model (SEM) analysis ascertained that the shifts of bacterial communities determined the changes of RS-SIR in both soils. The rate of bacterial community variance was significantly lower in non-copper-stressed soil compared to the other two copper-stressed (medium and high) soils, which might lead to the higher RS-SIR in the fluvo-aquic soil. As for the red soil, the substantial increase of the dominant group WPS-2 after DW disturbance might result in the low RS-SIR in the high copper-stressed soil. Moreover, in both soils, the bacterial diversity was highest in non-copper-stressed soils. Our results revealed that initial copper stress could decrease the resistance of soil microbial community structure and function to subsequent DW disturbance.

[Tobacco cadmium health risk assessment and reduction techniques: A review].

Tobacco is one of the cadmium accumulation and tolerance plants. Decreasing cadmium content of tobacco contributes to environmental safety and human health. Three aspects on tobacco cadmium research were reviewed in this paper, i.e. uptake and distribution of cadmium in tobacco, and health risk assessment of cadmium in tobacco and reduction measures. The current situations and existing challenges in the research field were discussed. The cadmium tolerance mechanisms of tobacco were reviewed, the factors on cadmium uptake were analyzed, and the general distribution of cadmium in tobacco was summarized. From the point of health risk assessment, the lack of cadmium limits in tobacco was identified, the recommended formula to calculate cadmium limits of tobacco based on atmosphere cadmium limits and digestion cadmium limits was provided and the cadmium limits of tobacco were estimated using each formula, and suggestions on cadmium limits in tobacco were presented. At last, we put forward several effective reduction measures to lower cadmium level in tobacco leaves.

Long-term nickel exposure altered the bacterial community composition but not diversity in two contrasting agricultural soils.

Nickel pollution imposes deleterious effects on soil ecosystem. The responses of soil microorganisms to long-term nickel pollution under field conditions remain largely unknown. Here, we used high-throughput sequencing to elucidate the impacts of long-term nickel pollution on soil bacterial communities in two contrasting agricultural soils. Our results found that the soil microbial biomass carbon consistently decreased along the nickel gradients in both soils. Nickel pollution selectively favored or impeded the prevalence of several dominant bacterial guilds, in particular, Actinobacteria showed tolerance, while Acidobacteria and Planctomycetes displayed sensitivity. Despite the apparent shifts in the bacterial community composition, no clear tendency in the bacterial diversity and abundance was identified along the nickel gradients in either soil. Collectively, we provide evidence that long-term nickel pollution shifted the soil bacterial communities, resulting in the decrease of microbial biomass although the bacterial diversity was not significantly changed.

Field-based evidence for consistent responses of bacterial communities to copper contamination in two contrasting agricultural soils.

Copper contamination on China's arable land could pose severe economic, ecological and healthy consequences in the coming decades. As the drivers in maintaining ecosystem functioning, the responses of soil microorganisms to long-term copper contamination in different soil ecosystems are still debated. This study investigated the impacts of copper gradients on soil bacterial communities in two agricultural fields with contrasting soil properties. Our results revealed consistent reduction in soil microbial biomass carbon (SMBC) with increasing copper levels in both soils, coupled by significant declines in bacterial abundance in most cases. Despite of contrasting bacterial community structures between the two soils, the bacterial diversity in the copper-contaminated soils showed considerably decreasing patterns when copper levels elevated. High-throughput sequencing revealed copper selection for major bacterial guilds, in particular, Actinobacteria showed tolerance, while Acidobacteria and Chloroflexi were highly sensitive to copper. The thresholds that bacterial communities changed sharply were 800 and 200 added copper mg kg(-1) in the fluvo-aquic soil and red soil, respectively, which were similar to the toxicity thresholds (EC50 values) characterized by SMBC. Structural equation model (SEM) analysis ascertained that the shifts of bacterial community composition and diversity were closely related with the changes of SMBC in both soils. Our results provide field-based evidence that copper contamination exhibits consistently negative impacts on soil bacterial communities, and the shifts of bacterial communities could have largely determined the variations of the microbial biomass.

Different influences of field aging on nickel toxicity to Folsomia candida in two types of soil.

Metal aging in soils has been considered an important factor influencing its availability and toxicity to organisms. In this study, we report the influence of 5 years field aging on the nickel (Ni) toxicity to collembolan Folsomia candida based on two different types of soil from Dezhou (DZ) and Qiyang (QY) counties in China. Acute and chronic toxicity of Ni to F. candida was assessed in both freshly spiked and field aging contaminated soils. We found that 5 years field aging increased the EC50 and 2d-LC50 values of Ni to F. candida in the DZ soil, while little influence on the Ni toxicity was observed in the QY soil. There was no adverse effect of the long-term field aging on the Ni toxicity to the survival of F. candida in the two tested soils. In addition, field aging of the two soils impacted differently the water-soluble Ni concentrations, which were significantly correlated to the juvenile production of F. candida based on a logistic model. Our study highlights different effects of long-term field aging on the Ni toxicity to F. candida between divergent types of soil, and this should be taken into account in future toxicity testing and risk assessment practices.

[Effects of long-term fertilization on evolution of S forms in a red soil and a black soil].

Sulfur (S) forms in two contrasting soils (a red soil and a black soil) under different long-term fertilization treatments (from 1990 to 2011) from the National Long-term Monitoring Network of Soil Fertility and Fertilizer Effects of China were investigated using a fractionation scheme in order to explore the distribution and transportation of S with different forms in the soils. The soil samples were collected from the topsoil (0-20 cm) and subsoil (20-40 cm) horizons that were treated with no fertilizers (CK), nitrogen, phosphorus, and potassium fertilizers (NPK), or NPK plus organic manures (MNPK) since 1990. The results indicated that when compared with the CK, total S contents in the topsoil layers treated with NPK and MNPK were increased by 42% and 33% for the red soil, and by 6% and 76% for the black soil, respectively, while the total S in the subsoil layer was less affected by the fertilization treatments and obviously lower than in the topsoil layer except for the red soil treated with NPK. The main forms of inorganic S in the red soil and black soil were found to be available S and HCl-extracted S, respectively. The application of NPK and MNPK increased the available S by 447% and 102% in the topsoil layer of the red soil compared with CK, and facilitated the transportation of available S into the lower depth. In contrast, NPK and MNPK only increased the available S by 54% and 93% in the topsoil layer of the black soil, and showed a slight influence on available S in the subsoil. The organic S forms were predominantly composed of ester S and residual S in the two soils. Under long-term fertilization, the residual S significantly increased over 32% and 55% in the topsoil and subsoil layers, respectively, compared with CK. The ester S and carbon-bonded S, which were relatively active, were less affected by the fertilization treatments, but positively related to the level of organic carbon in each soil (P < 0.05). In addition, the results from the long-term experiments indicated that the contribution of S input from atmospheric deposition was significant and should not be neglected.

Field dissipation of four personal care products in biosolids-amended soils in North China.

The present study investigated the dissipation behaviors of 4 typical personal care products (PCPs)-triclocarban (TCC), triclosan (TCS), tonalide (AHTN), and galaxolide (HHCB)- in soils amended with biosolids under field conditions in North China. The results showed that the 4 target compounds were detected in all biosolids-amended soils at levels of a few nanograms per gram to thousands of nanograms per gram (dry wt). The residual concentrations of the 4 PCPs were found in the following order: TCC > TCS > AHTN > HHCB. Significant dissipation of the 4 PCPs was observed in the biosolids-amended soils, with half-lives ranging from 26 d to 133 d. Furthermore, repeated biosolids applications and a higher biosolids application rate could lead to higher accumulation of the 4 PCPs in the agricultural soils. Based on the detected concentrations in the field trial and limited ecotoxicity data, high risks to soil organisms are expected for TCC, whereas low to medium risks are expected in most cases for AHTN, HHCB, and TCS.

Occurrence and dissipation of benzotriazoles and benzotriazole ultraviolet stabilizers in biosolid-amended soils.

Benzotriazoles (BTs) and benzotriazole ultraviolet (UV) stabilizers (BUVSs) are commonly used industrial and household chemicals, but little is known about their dissipation behavior in the soil environment associated with biosolid application. The authors investigated the occurrence and dissipation of 4 BTs (BT, 5-methyl-1H-benzotriazole [5-TT], 5-chloro-1H-benzotriazole [CBT], and 5,6-dimethyl-1H-benzotriazole [XT]) and 5 BUVSs (UV-326, UV-327, UV-328, UV-329, and UV-P) in biosolid-amended soil of 3 trial sites (Zhejiang, Hunan, and Shandong) in China following 2 treatments (treatment 1: a single application of biosolid; treatment 2: repeated application of biosolid). The results showed that except for CBT and XT, the other 7 compounds could be detected in most of the biosolid and biosolid-amended soils at levels of a few to tens of nanograms per gram and that the concentrations of the 7 compounds for treatment 2 were obviously higher than those for treatment 1. In the 1-yr monitoring of the Shandong site, 2 BTs (BT and 5-TT) and 5 BUVSs (UV-326, UV-327, UV-328, UV-329, and UV-P) were significantly dissipated in the biosolid-amended soils. The field half-lives of BT and 5-TT ranged from 217 d to 345 d, while those for the BUVSs ranged between 75 d and 218 d. The field half-lives of target compounds in soil were found to be comparable to the modeling results. The results suggest the persistence of BTs and BUVSs in soil environments with quite slow dissipation rates.

Initial copper stress strengthens the resistance of soil microorganisms to a subsequent copper stress.

To improve the prediction of essential ecosystem functioning under future environmental disturbances, it is of significance to identify responses of soil microorganisms to environmental stresses. In this study, we collected polluted soil samples from field plots with eight copper levels ranging from 0 to 3,200 mg Cu kg(-1) soil. Then, the soils with 0 and 3,200 mg Cu kg(-1) were selected to construct a microcosm experiment. Four treatments were set up including Cu0-C and Cu3200-C without further Cu addition, and Cu0-A and Cu3200-A with addition of 57.5 mg Cu kg(-1) soil. We measured substrate-induced respiration (SIR) and potential nitrification rate (PNR). Furthermore, the abundance of bacterial, archaeal 16S rRNA genes, ammonia-oxidizing bacteria and archaea amoA genes were determined through quantitative PCR. The soil microbial communities were investigated by terminal restriction fragment length polymorphism (T-RFLP). For the field samples, the SIR and PNR as well as the abundance of soil microorganisms varied significantly between eight copper levels. Soil microbial communities highly differed between the low and high copper stress. In the microcosm experiment, the PNR and SIR both recovered while the abundance of soil microorganisms varied irregularly during the 90-day incubation. The differences of microbial communities measured by pairwise Bray-Curtis dissimilarities between Cu0-A and Cu0-C on day 0 were significantly higher after subsequent stress than before. However, the differences of microbial communities between Cu3200-A and Cu3200-C on day 0 changed little between after subsequent stress and before. Therefore, initial copper stress could increase the resistance of soil microorganisms to subsequent copper stress.

Field dissipation and plant uptake of benzotriazole ultraviolet stabilizers in biosolid-amended soils.

Benzotriazole ultraviolet stabilizers (BUVSs) have been commonly used in industrial and household product formulations, and have been detected in biosolids from wastewater treatment plants. However, little is known about their occurrence and dissipation behavior in the soil environment associated with biosolid application. This study investigated the occurrence and dissipation of five typical BUVSs (UV-326, UV-327, UV-328, UV-329 and UV-P) in biosolid-amended soils, and the uptake of these biocides by plants. The field trial includes two treatment groups: old groups with biosolid application at rates of 5, 10, 20 and 40 t ha(-1) every year within 5 years, and new groups with only one biosolid application. The results showed that the five BUVSs could be detected in most biosolid-amended soils at a few to tens of ng g(-1) levels, but not detected in the control soils. These chemicals were not found in the crop plants collected from the trial plots. Moreover, high biosolid application rates and repeated biosolid applications resulted in high accumulation of these BUVSs in soil. During one year monitoring, the five BUVSs were significantly dissipated in the biosolid-amended soils with their half-lives ranging from 79 to 223 days, which were comparable with the modeling results. The results from this study demonstrated the persistence of BUVSs in soil environments with quite slow dissipation rates.

Field dissipation and risk assessment of typical personal care products TCC, TCS, AHTN and HHCB in biosolid-amended soils.

The antimicrobial agents triclocarban (TCC) and triclosan (TCS) and synthetic musks AHTN (Tonalide) and HHCB (Galaxolide) are widely used in many personal care products. These compounds may release into the soil environment through biosolid application to agricultural land and potentially affect soil organisms. This paper aimed to investigate accumulation, dissipation and potential risks of TCC, TCS, AHTN and HHCB in biosolid-amended soils of the three field trial sites (Zhejiang, Hunan and Shandong) with three treatments (CK: control without biosolid application, T1: single biosolid application, T2: repeated biosolid application every year). The one-year monitoring results showed that biosolids application could lead to accumulation of these four chemicals in the biosolid-amended soils, with the residual concentrations in the following order: TCC>TCS>AHTN>HHCB. Dissipation of TCC, TCS, AHTN and HHCB in the biosolid-amended soils followed the first-order kinetics model. Half-lives for TCC, TCS, AHTN and HHCB under the field conditions of Shandong site were 191, 258, 336 and 900 days for T1, and 51, 106, 159 and 83 days for T2, respectively. Repeated applications of biosolid led to accumulation of these personal care products and result in higher ecological risks. Based on the residual levels in the trial sites and limited toxicity data, high risks to soil organisms are expected for TCC and TCS, while low-medium risks for AHTN and HHCB.

[Effects of aging time on the form transformation and eco-toxicity threshold (ECx) of added Zn in typical China soils].

Six typical China soils with different properties were selected and added with seven concentrations of ZnCl2 to study the effects of different aging time (14, 90, 180, 360, and 540 days) on the form transformation and eco-toxicity threshold (ECx) of added Zn in the soils, with the main affecting factors analyzed. The results indicated that with the increase of aging time, the fraction of 0.01 mol x L(-1) CaCl2-extracted Zn in the soils decreased sharply initially, then slowed down, and reached the dynamic balance after 540 d incubation. The eco-toxicity thresholds (ECx, x = 10, 50) of Zn to bok choy increased significantly with aging time (P < 0.05), which implied the marked decrease of the phyto-toxicity of Zn. The measured aging factors AF10 and AF50 of Zn ranged from 1.077-1.743 and 1.174-1.441, respectively, and increased with aging time. The balanced concentration of Zn in the soils was significantly negatively correlated with soil pH, CEC, and organic carbon (Org-C) content, and soil pH was the most important controlling factor, followed by CEC and Org-C. It took shorter time to reach Zn balance in the soils with higher pH. The prediction model of the ECx of Zn was developed based on the aging factors and the main soil properties, and could be well validated by the measured ECx under field condition. This study would provide theoretical basis for the normalization of the eco-toxicity thresholds of added Zn in different soils and the formulation of the environmental criterion of Zn in China soils.

Typical azole biocides in biosolid-amended soils and plants following biosolid applications.

Biosolid application on agricultural land may contaminate soils with various household chemicals and personal care products. This study investigated the occurrence and dissipation of typical azole biocides climbazole, clotrimazole, and miconazole in biosolid-amended soils as well as the uptake of these biocides by plants. The field trial includes two treatment groups: old groups with biosolid application at rates of 5, 10, 20, and 40 t/ha every year within 5 years, and new groups with only one biosolid application. The results showed that climbazole, clotrimazole, and miconazole were detected in biosolid-amended soils, but not detected in control soils. These biocides were not found in the crop plants collected from the trial plots. The dissipation half-lives for climbazole, clotrimazole, and miconazole under the field conditions were 175-179, 244, and 130-248 days, respectively. High biosolid application rates and repeated biosolid applications could lead to higher persistence of the biocides in the agricultural soils. An exposure model could effectively predict the residual concentrations of climbazole and miconazole in the biosolid-amended soils of the old treatments with different biosolid application rates. Thus, the field trial demonstrated high persistence of these three biocides in the soil environments.

Occurrence and dissipation of three azole biocides climbazole, clotrimazole and miconazole in biosolid-amended soils.

This study investigated the occurrence and dissipation of three azole biocides climbazole, clotrimazole and miconazole in biosolid-amended soils of the three sites (Zhejiang, Hunan and Shandong) in China following three treatments (CK: control without biosolid application; T1: one biosolid application; T2: biosolid application every year). The results showed that climbazole, clotrimazole and miconazole were present in the biosolid and biosolid-amended soils, but absent in the control soils. In the soils treated with biosolids, the concentrations of climbazole, clotrimazole and miconazole were mostly lower in the Zhejiang soils than in the Shandong or Hunan soils, suggesting that these three biocides are more readily dissipated under the flooding condition. During the one year monitoring, the concentrations of climbazole, clotrimazole and miconazole in the biosolid-applied soils showed only slight variations. The dissipation half-lives for miconazole calculated under the field conditions of Shandong site were 440 days for T1 and the half-lives for clotrimazole were 365 days for T2. The results suggested the persistence of these three biocides in the soil environments.

[Toxicity and accumulation of copper and nickel in wheat plants cropped on alkaline and acidic field soils].

Field experiments were conducted to study the toxicity of added copper (Cu) and nickel (Ni) in soils to wheat and metal accumulation in wheat plants. The results showed that the yields of wheat straw and grain were decreased with the increasing concentration of Cu and Ni added to soils. The added Cu concentrations yielding 10% inhibition of wheat yield (EC10) were 499.6 mg x kg(-1) for alkaline soils (Dezhou, pH 8.90), and 55.7 mg x kg(-1) for acidic soils (Qiyang, pH 5.31). The toxicity of Cu or Ni in acidic soils were significantly higher than that in alkaline soils. With increasing addition of Cu or Ni, the contents of Cu in wheat grains initially increased and then keep at constant level, while the accumulation of Ni in grains linearly increased. The contents of Cu and Ni in Qiyang wheat grains were 6.07-9.26 mg x kg(-1) and 0.53-31.78 mg x kg(-1), and those of in Dezhou were 5.24-10. 52 mg x kg(-1) and 0.16-25.33 mg x kg(-1). In both field experimental sites, the contents of Cu in wheat grains meet the national standard for food safety. These findings showed that Cu is more relevant to ecological risk assessments than to food safety assessments for wheat grown in soils that have been contaminated with Cu.