Trace element accumulation from swine feeds to feces in Chinese swine farms: Implication for element limits.

Trace elements like copper and zinc are supplemented in swine feeds to suppress bacteria and/or promote growth. Due to low absorption rates, trace elements are highly concentrated in swine feces, posing a risk to soil and human health if applied to agricultural fields. In the present study, the concentrations of six trace elements (Cu, Zn, As, Cd, Pb, and Cr) in pig feed and feces were evaluated by sample analysis and data from the literature. The feed-to-feces and feces-to-compost enrichment factors of the trace elements were determined to back-calculate safe concentrations in feed needed to meet permissible trace element concentrations in organic fertilizers. The Cu and Zn concentrations in feeds were the highest, being statistically significantly higher in starter pig feeds than in grower-finisher feeds. Copper exceeded feed limits mainly in the feeds of finisher pigs and sows, while exceedance for Zn occurred in almost all feed samples. Concentrations above the limits were also observed for Pb and Cr impurities in mineral feed supplements. The highest Cu and Zn concentrations in feces were observed for starter pigs. Moreover, significant enrichment of trace elements from feeds to feces was found, with enrichment factors calculated as: 4.68-6.11 for Cu, 3.43-4.60 for Zn, 2.30-3.12 for As, 2.89-4.63 for Cd, 2.45-5.00 for Pb, and 3.32-5.00 for Cr. On this basis, the recommended calculated limits for Cu, Zn, As, Cd, Pb, and Cr in feeds for different ages of pigs were 41-53, 130-175, 2-3, 0.3-0.5, 5-10, and 15-23 mg/kg, respectively. Priority index calculations and the calculated recommended limits indicated that Cu in starter pig feeds and Cd in starter and breeding pig feeds should be prioritized for reduction to enable feces compost to be utilized safely in agricultural land amendment. Integr Environ Assess Manag 2022;18:978-987. © 2021 SETAC.

Intrinsic soil property effects on Cd phytotoxicity to Ligustrum japonicum 'Howardii' expressed as different fractions of Cd in forest soils.

A better comprehensive understanding of the influence of soil/solution properties on cadmium (Cd) phytotoxicity is essential for soil Cd ecological risk assessment. The toxicity of soil spiked Cd to Ligustrum japonicum 'Howardii' seedling growth was conducted by the greenhouse pot experiments using 13 typical forest soils selected from mainland of China. The results showed that the ranges of Cd toxicity thresholds of 10% seedling growth inhibition (EC10) and 50% inhibition (EC50) followed the order: soil pore water Cd (EC10 on average 0.88 mg L-1 with the variation of 54.9 folds and EC50 on average 2.28 mg L-1 with variation of 41.8 folds), DTPA extractable Cd (EC10 on average 5.4 mg kg-1 with 20.9 folds variation and EC50 on average 17.86 mg kg-1 with 6.6 folds variation), total added Cd (EC10 on average 6.55 mg kg-1 with 16.7 folds variation and EC50 on average 22.11 mg kg-1 with 5.1 folds variation), which suggested that whatever the available Cd expressed, its toxicity is largely affected by soil properties. The empirical multiple equations were well developed between different fractions of Cd toxicity thresholds ECx (x = 10 or 50) and soil/solution. The results also showed that the pH inversely correlated with EC10 (r2 = 0.54, P < 0.01) and EC50 (r2 = 0.63, P < 0.001) based on soil pore water, indicating the ECx decreased with more toxicity as pH increased. No single significant soil solution properties were found for ECx in DTPA extractable Cd. For the ECx of DTPA extractable and total Cd, the content of aluminum oxides in soil and soil pH were the two significant factors inversely related with ECx, which explained 68%-79% of the inter-soil variation, respectively. Overall, soil or solution pH was the most important factor controlling Cd toxicity thresholds. Meanwhile, significant negative correlations existed between the soil solution pH and the slopes of parameter (b) of the dose-response curves for different fractions of Cd, implying that the growth of toxic effect enhanced as unit Cd dosage increased in low pH soils. These results will be helpful to evaluate the metal ecological risk in forest soils.

A new model integrating short- and long-term aging of copper added to soils.

Aging refers to the processes by which the bioavailability/toxicity, isotopic exchangeability, and extractability of metals added to soils decline overtime. We studied the characteristics of the aging process in copper (Cu) added to soils and the factors that affect this process. Then we developed a semi-mechanistic model to predict the lability of Cu during the aging process with descriptions of the diffusion process using complementary error function. In the previous studies, two semi-mechanistic models to separately predict short-term and long-term aging of Cu added to soils were developed with individual descriptions of the diffusion process. In the short-term model, the diffusion process was linearly related to the square root of incubation time (t1/2), and in the long-term model, the diffusion process was linearly related to the natural logarithm of incubation time (lnt). Both models could predict short-term or long-term aging processes separately, but could not predict the short- and long-term aging processes by one model. By analyzing and combining the two models, we found that the short- and long-term behaviors of the diffusion process could be described adequately using the complementary error function. The effect of temperature on the diffusion process was obtained in this model as well. The model can predict the aging process continuously based on four factors-soil pH, incubation time, soil organic matter content and temperature.

Derivation of soil thresholds for lead applying species sensitivity distribution: A case study for root vegetables.

The combination of food quality standard and soil-plant transfer models can be used to derive critical limits of heavy metals for agricultural soils. In this paper, a robust methodology is presented, taking the variations of plant species and cultivars and soil properties into account to derive soil thresholds for lead (Pb) applying species sensitivity distribution (SSD). Three species of root vegetables (four cultivars each for radish, carrot, and potato) were selected to investigate their sensitivity differences for accumulating Pb through greenhouse experiment. Empirical soil-plant transfer model was developed from carrot New Kuroda grown in twenty-one soils covering a wide variation in physicochemical properties and was used to normalize the bioaccumulation data of non-model cultivars. The relationship was then validated to be reliable and would not cause over-protection using data from field experimental sites and published independent studies. The added hazardous concentration for protecting 95% of the cultivars not exceeding the food quality standard (HC5add) were then calculated from the Burr Type III function fitted SSD curves. The derived soil Pb thresholds based on the added risk approach (total soil concentration subtracting the natural background part) were presented as continuous or scenario criteria depending on the combination of soil pH and CEC.

[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.