Occurrence and distribution of heavy metals and tetracyclines in agricultural soils after typical land use change in east China

摘要

Land use in east China tends to change from paddy rice to vegetables or other high-value cash crops, resulting in high input rates of organic manures and increased risk of contamination with both heavy metals (HMs) and antibiotics. This investigation was conducted to determine the accumula tion, distribution and risks of HMs and tetracyclines (TCs) in surface soils and profiles receiving different amounts of farm yard manure. Soil samples collected from suburbs of Hangzhou city, Zhejiang province were introduced to repre sent three types of land use change from paddy rice to aspar agus production, vineyards and field mustard cultivation, and divided into two portions, one of which was air-dried and sieved through 2-, 0.3- and 0.149-mm nylon mesh for deter mination of pH and heavy metals. The other portion was frozen at -20 ℃, freeze-dried and sieved through a 0.3-mm nylon mesh for tetracyline determination. HM and TC con centrations in surface soils of 14-year-old mustard fields were the highest with total Cu, Zn, Cd and ∑TCs of 50.5, 196,1.03 mgkg~(-1) and 22.9 μgkg~(-1), respectively, on average. The total Cu sequence was field mustard>vineyards>asparagus when duration of land use change was considered; oxytetra-cycline (OTC) and doxycycline were dominant in soils used for asparagus production; OTC was dominant in vineyards and chlortetracycline (CTC) was dominant in mustard soils. There were positive pollution relationships among Cu, Zn and ∑TCs, especially between Cu and Zn or Cu and ∑TCs. Repeated and excessive application of manures from intensive farming systems may produce combined contamination with HMs and TCs which were found in the top 20 cm of the arable soil profiles and also extended to 20-40 cm depth. Increasing manure application rate and cultivation time led to continuing increases in residue concentrations and movement down the soil profile.