Livestock keratin waste is a rich source of protein. However, the unique structure of livestock keratin waste makes its valorization a great challenge. This paper reviews the main methods for the valorization of livestock keratin waste, which include chemical, biological, and other novel methods, and summarizes the main agricultural applications of keratin-based material. Livestock keratin waste is mainly used as animal feed and fertilizer. However, it has promising potential for biosorbents and in other fields. In the future, researchers should focus on the biological extraction and carbonization methods of processing and keratin-based biosorbents for the soil remediation of farmland.

The co-transport of contaminants by soil colloids can generate substantial environmental risk, and this behavior is greatly affected by environmental conditions. In this study, AF4-ICP-MS was used to investigate the size distribution and composition of Cd/Pb-bearing colloids; saturated sand column experiments were used to investigate the impact of soil colloids on the transport of Cd/Pb under different pH and ionic strength conditions. AF4-ICP-MS characterization showed that natural colloids were primarily associated with two sizes ranges: 0.3–35 KDa (F1, fine nanoparticles) and 280 KDa–450 nm (F2, larger nanoparticles), which mainly consisted of organic matter (OM), iron (Fe), and manganese (Mn) (oxy)hydroxides and clay minerals. Fine nanoparticles could strongly adsorb Cd and Pb under all environmental conditions. Mn and Fe (oxy)hydroxides generally formed under neutral to alkaline conditions and exhibited adsorption capabilities for Cd and Pb, respectively. Transport experiments were conducted under different pH and ionic strength conditions. At pH 3.0, soil colloids had little effect on the transport of Cd²⁺ and Pb²⁺. At pH 5.0, soil colloids inhibited the transport of Cd²⁺ by 16.1%, and Pb²⁺ recovery was still 0.0%. At pH 7.0 and 9.0, soil colloids facilitated the transport of Cd²⁺ by 15.6% and 29.6%, facilitated Pb²⁺ by 1.3% and 6.4%. At an ionic strength of 0, 0.005, and 0.01 mol L⁻¹ NaNO₃, soil colloids facilitated the transport of Cd²⁺ by 77.7%, 45.8%, and 15.6%, only facilitated the transport of Pb²⁺ by 46.2% at an ionic strength of 0 mol L⁻¹ NaNO₃. At an ionic strength of 0.05 mol L⁻¹ NaNO₃, soil colloids inhibited the transport of Cd²⁺ and Pb²⁺ by 33.1% and 21.0%, respectively. The transport of Cd²⁺ and Pb²⁺ facilitated by soil colloids was clearly observed under low ionic strength and non-acidic conditions, which can generate a potential environmental risk.

We found that the typical fluoroquinolone antibiotic enrofloxacin (ENR) and plasticizer di-(2-ethylhexyl) phthalate (DEHP) are often detected simultaneously and at high frequencies in the environment, but their combined exposure effects on soil animals are poorly understood. Here, oxidative stress, DNA damage and changes in digestibility of the earthworm were investigated to reflect the toxicological effects of single and combined exposure of DEHP and ENR on earthworms (Eisenia fetida). We found that the DEHP treatment group and the combined pollution treatment group showed significantly increased reactive oxygen species content of earthworms at 14 d and 28 d. ENR exposure alone had little effect on the antioxidant enzyme system, while DEHP and combined treatment showed a trend of inhibition and then activation. Addition of both pollutants caused a rise in the lipid peroxidation levels of earthworms. Malonaldehyde (MDA) was mainly scavenged by glutathione sulfur transferase (GST). ENR and DEHP caused more DNA damage to earthworm tissue than their combined pollution under the regulation of GST. Both single and combined pollution inhibited the digestive enzyme activity of earthworms, but the combined pollution had a stronger inhibitory effect. Cellulase, MDA and GST were the three most sensitive indicators on PCA. The toxicity was ENR + DEHP > DEHP > ENR according to the IBR index, and the combined toxicity showed a synergistic effect. The results showed that the combined pollution of phthalate esters and antibiotics in the actual environment was a significant ecological risk that deserves special attention.

Returning livestock manure to the cropland as organic fertilizer is a sustainable and environmentally friendly treatment method, but its application also alters the soil microenvironment. However, the impact of soil microbial community disturbance and pollutant accumulation from different types of organic fertilizers remains largely unknown in South China. To fill this gap, we investigated the effects of organic fertilizers, including chicken manure, pig manure and vermicompost on the soil bacterial and fungal communities and environmental risks. The results show that applying organic fertilizer effectively increases the soil nutrient content. High-throughput sequencing of bacteria and fungi showed that the application of different organic fertilizers had differential effects on microbial community structure, with the highest number of microbe-specific OTUs in the vermicomposting treatment. Additionally, this study found no risk of heavy metal (Cu, Zn, Pb, Cr and Cd) contamination from short-term organic fertilizer application, but there was a risk of antibiotic (ENR and CHL) contamination. Functional microorganisms regulating heavy metals and antibiotics were identified by RDA analysis. This study facilitates the screening of types of organic fertilizers that can be safely returned to the field as well as developing strategies to regulate functional microbes.