Field study on loss of tetracycline antibiotics from manure-applied soil and their risk assessment in regional water environment of Guangzhou, China.

Tetracycline antibiotics (TCs) introduced into agricultural fields via manure application tend to accumulate in soils and further reach water environments via surface runoff and leachate, posing potential risks to regional water environment. This study investigated the loss of tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC) in surface runoff and leachate samples collected from a vegetable farmland with manure application in Guangzhou, South China. A risk assessment method was constructed for evaluating the ecological and health risks of manure-associated antibiotics released from soil into water environment. The results showed that the concentrations of three TCs in surface runoff, 30-cm leachate, and 60-cm leachate after the first rainfall event were 2.79-35.97, 1.71-18.44, and 0.4-2.66 µg/L, respectively, which all decreased with sampling depth and the time after rainfall events. Up to 0.13% of TCs were transported into the surface water through surface runoff, while less than 0.01% of TCs were transported into the groundwater through leachate at 60 cm. OTC had a higher total mass percentage (0.13%) into surface water via runoff than CTC (0.11%) and TC (0.07%) likely due to its smallest Kd value and largest input mass. Based on loss percentages, their predicted environmental concentrations (PEC) ranged from 4.87 (TC) to 16.91 (OTC) ng/L in regional surface water and 1.42 (TC) to 5.20 (CTC) ng/L in regional groundwater. The risk assessment based on PEC results suggested non-negligible health risk (HQ > 1.0 × 10-6) and low ecological risk (RQ < 0.1) in both regional surface water and groundwater, drawing concerns on the potential hazards of TCs released from manure-amended soil into water environments.

Colloidal stability of nanosized activated carbon in aquatic systems: Effects of pH, electrolytes, and macromolecules.

Nanosized activated carbon (NAC) is a novel adsorbent with great potential for water reclamation. However, its transport and reactivity in aqueous environments may be greatly affected by its stability against aggregation. This study investigated the colloidal stability of NAC in model aqueous systems with broad background solution chemistries including 7 electrolytes (NaCl, NaNO3, Na2SO4, KCl, CaCl2, MgCl2, and BaCl2), pH 4-9, and 6 macromolecules (humic acid (HA), fulvic acid (FA), cellulose (CEL), bovine serum albumin (BSA), alginate (ALG), and extracellular polymeric substance (EPS)), along with natural water samples collected from pristine to polluted rivers. The results showed that higher solution pH stabilized NAC by raising the critical coagulation concentration from 28 to 590 mM NaCl. Increased cation concentration destabilized NAC by charge screening, with the cationic influence following Ba2+ > Ca2+ > Mg2+ >> Na+ > K+. Its aggregation behavior could be predicted with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory with a Hamaker constant (ACWC) of 4.3 × 10-20 J. The presence of macromolecules stabilized NAC in NaCl solution and most CaCl2 solution following EPS > BSA > CEL > HA > FA > ALG, due largely to enhanced electrical repulsion and steric hindrance originated from adsorbed macromolecules. However, ALG and HA strongly destabilized NAC via cation bridging at high Ca2+ concentrations. Approximately half of NAC particles remained stably suspended for ∼10 d in neutral freshwater samples. The results demonstrated the complex effects of water chemistry on fate and transport of NAC in aquatic environments.

Occurrence and distribution of natural and synthetic progestins, androgens, and estrogens in soils from agricultural production areas in China.

The occurrence of biologically potent sex hormones in agricultural soils is of growing concern due to their ability to disrupt the endocrine systems of aquatic organisms after being transported to surface waters via runoff. This study, therefore, examined the large-scale occurrence of 34 natural and synthetic sex hormones (13 progestins, 16 androgens, and 5 estrogens) in soils from 7 provinces and 1 municipality in China. The target sex hormones were detected in 99.3% of the soil samples, indicating their widespread occurrence in most agricultural areas. Additionally, seven synthetic progestins were detected in soils for the first time. The total concentration of the 34 sex hormones (Σsex hormones) in the sampled soils ranged from below the method detection limit to 23.7 ng/g (mean of 4.72 ± 4.07 ng/g), with androgens and progestins being the most dominant hormone groups. Significant correlations were observed among the concentrations of Σestrogens, Σandrogens, and Σprogestins (r = 0.117-0.433, p < 0.001), suggesting similar sources of sex hormones. The mean concentration of Σsex hormones varied considerably across the selected provinces/municipality. Notably, the annual slaughter of poultry and swine (R2 = 0.75-0.88), female population (R2 = 0.57-0.58), and soil organic carbon content (R2 = 0.20-0.55) in each province were significantly correlated with the concentrations or mean concentrations of Σsex hormones, Σestrogens, or Σprogestins. This finding implies that these parameters contributed to the occurrence and distribution of sex hormones in the studied soils. Finally, risk quotients for some sex hormones exceeded 0.01, indicating medium or high risks to agroecosystems. This study highlights the importance of designing an optimal manure fertilization strategy in order to mitigate the risks posed by sex hormones in agroecosystems.

Runoff Losses in Nitrogen and Phosphorus From Paddy and Maize Cropping Systems: A Field Study in Dongjiang Basin, South China.

Surface runoff is one of the predominant routes for agricultural nitrogen (N) and phosphorus (P) losses, yet their characteristics and corresponding control measures are not fully understood. In 2019 and 2020, field-scale plot experiments were performed at Dongjiang Basin in South China to investigate the characteristics of N and P runoff losses from paddy and maize cropping systems. The results showed that N and P losses from maize fields via surface runoff (27.85 and 1.24 kg ha-1 year-1) were significantly higher than those from paddy fields (15.37 and 0.8 kg ha-1 year-1). The main forms of N losses were nitrate ( NO 3 - -N) and ammonium ( NH 4 + -N) in paddy and maize fields, respectively, whereas particulate P form predominated in surface runoff losses from both the paddy and maize fields. Considerable proportions of agricultural N and P (71-83% of the total runoff loss) were lost during basal fertilization and first topdressing application. Moreover, frequent rainfall events following fertilizer application triggered N and P losses from the monitored fields. About 26.22 and 37.48% of N fertilizer was recovered from grains and straw of paddy and maize, respectively, whereas only 12.35 and 19.51% of P fertilizer were recovered during the crop harvesting stage. Surface runoff was one of the dominant liquid pathways in N loss, whereas most of P loss (introduced from fertilizers without crops utilization) was fixed in the soil. Principal component analysis (PCA) proved that the primary sources of N and P losses were fertilizers rather than N and P in the soil. The current results suggest controlled management relating to fertilization, irrigation, and tillage strategies are effective measures for reducing N and P losses, thereby controlling agricultural non-point source pollution. It is hoped that this study will provide comprehensive field-based inputs on characteristics of N and P runoff losses and formulate appropriate control strategies to protect aquatic environments from eutrophication.