In this paper, using the leaching models, we quantified the leaching content of Cd, Pb, Cu, and Zn, and estimated the ecological risk changes in farmland soil caused by leaching and the ecological risk in leachate in China. Jiangxi, Guangxi, Guizhou, Hainan, Hunan, Zhejiang, Guangdong, and Chongqing are hotspot areas. The leaching of Cd in these regions exceed reported mean values in Europe (2.56 g ha⁻¹ year⁻¹). Although the total ecological risk of heavy metals in the soil of various provinces (ranged from 20 to 130) was generally low, Cd was the most important contributor to ecological risks, while 9 provinces exhibited considerable ecological risk from Cd. The calculated Cd, Pb, and Zn in leachate exceed drinking water standards (GB 5749-2022) in five provinces. Overall, the leaching of heavy metals in Chinese agricultural soils, particularly in the southern regions, is a critical issue that warrants attention. Soil pH is the most prominent factor influencing heavy metal leaching. A 5% increase in pH reduces leaching by 31.2% for Cd, 25.42% for Pb, 22.07% for Cu, and 38.37% for Zn. Adjusting the pH to 6 can effectively solve the problem of excessive heavy metal content in leachate in most areas. The study recommends prioritizing groundwater monitoring in critical provinces such as Jiangxi and adjusting the soil pH of farmland in key regions.

Background: Although hydrolysis and photolysis are important pathways for penicillin antibiotics degradation in aquatic ecosystems, the degradation mechanism of penicillin antibiotics in real natural waters is rarely reported. Furthermore, the dominant factors influencing this process are poorly understood. Methods: Therefore, five natural waters were selected to simulate both the hydrolysis and photolysis processes of penicillin G (PG) in aqueous environments. Results: Our results demonstrated that the half-life of PG hydrolysis ranged from 44 h to 141 h in natural water, and aqueous Ca²⁺ ion was the most important factor controlling the hydrolytic degradation of PG. Moreover, several biological dissolved organic matter (DOM, microbial by-product compounds) could also promote the PG hydrolysis reaction. Direct photolysis of PG is dominated in natural water, for which half-life photodegradation rates were 6 h in both blank and natural water, suggesting that salinity and DOM have little influence on penicillin photolysis. The hydrolysis reaction mainly involved the cleavage of the ester bond in the β-lactam ring and a decarboxylation process, while photolysis degradation principally included the hydroxylation of the benzene ring and destruction of the thiazole ring. Conclusions: This study demonstrates the significant factors influencing hydrolysis and photolysis of penicillin antibiotics in an aquatic ecosystem, which can improve the estimates of ecological risk of antibiotic pharmaceuticals in a realistic environment.