Comprehensive analysis of the fates and risks of veterinary antibiotics in a small ecosystem comprising a pig farm and its surroundings in Northeast China.

This study investigated the behavior of veterinary antibiotics (VAs) in a small farm ecosystem. Manure and environmental samples were collected around a large pig farm in northeast China. Thirty-four VAs in six categories were analyzed. Then, a multimedia fugacity model was used to estimate the fates of VAs in the environment. The results showed that VAs were prevalent in manure, soil, water, and sediment, but not in crops. Compared with fresh manure, VA levels were significantly lower in surface manure piles left in the open air for 3-6 months. The main VAs, tetracyclines and quinolones, decreased by 427.12 and 158.45 µg/kg, respectively. VAs from manure piles were transported to the surroundings and migrated vertically into deep soil. The concentrations of ∑VAs detected in agricultural soils were 0.03-4.60 µg/kg; > 94% of the mass inventory of the VAs was retained in soil organic matter (SOM), suggesting that SOM is the main reservoir for antibiotics in soil. Risk assessment and model analysis indicated that the negative impact of mixed antibiotics at low concentrations in farmland on crops may be mediated by indirect effects, rather than direct effects. Our findings highlight the environmental fates and risks of antibiotics from livestock farms.

[Effect of Decomposing Products of Immobilized Carriers on Desorption of Pyrene in Contaminated Soil].

Batch experiments were conducted to investigate the effect of soluble and insoluble decomposing products (decomposed for 1 day and 120 day; noted by DP1 and DP120, respectively) from immobilized carriers (corncob) on the desorption of pyrene in PAH-contaminated soil (120 d ageing, 20 mg x kg(-1)). It was found that (1) adding decomposing products of immobilized carriers could not only increase the rapidly desorbing fraction, but also improve the desorption rate of pyrene. The desorption rates of pyrene increased from 20% to 81.8% and 84.5% because of adding insoluble DP1 and DP120, and from 40% to 89.6% and 88.5% because of adding soluble DP1 and DP120. (2) The sorption amounts of pyrene by insoluble DP1 and.DP120 were 9. 4 and 16. 6 times higher than that by natural corncob, respectively. The sorption amounts of XAD-2 resins were increased by 1.5 and 3.1 times due to the added soluble DP1 and DP120, respectively. These results indicated that decomposing products of immobilized carries could improve the desorption of pyrene by sorption or activation in contaminated soil.

[Effects of root exudates of clover (Trifolium repens) on PAH microbial degradation and dioxygenase].

To demonstrate rhizospheric effect on the mechanism of (polycyclic aromatic hydrocarbon) PAH degradation, and to establish a proper joint phyto-microbial remediation mode, microcosms containing microorganisms and PAHs (pyrene and benzo[a]Pyrene) were added with clover (Trifolium repens) root exudates to study their effects on PAH degradation. Dioxygenase gene and 16S rDNA gene copy number changes during the biodegradation process were analyzed, and the microorganism with a good ability for degrading PAHs was identified. The results showed that Mycobacterium M1 had the capability to degrade PAHs. When total organic carbon (TOC) concentration of clover root exudates was 35.5 mg · L(-1), pyrene and benzo[a]pyrene degradation rates increased significantly, and the proportion of dioxygenase gene to 16S rDNA of Mycobacterium M1 increased. In the biodegradation process, dioxygenase gene copy number increased significantly, whereas 16S rDNA copy number increase was not so obvious, showing that the former was related to degradation process, but the latter was related to microbial numbers. It was concluded that the clover root exudates promoted the dioxygenase gene copy number of Mycobacterium M1, which contributed to the degradation of PAHs.