The Impact of Remediation Through Stabilizing Amendments on Taxonomic and Metabolic Patterns of Bacteria and Archaea in Cadmium-Contaminated Paddy Fields in Southwestern China

Abstract

42. during the period of irrigation, but be in an oxidation state when fields were in draining 43 and drying periods. The periodical alternation of wetting and drying forms unique 44 physical, chemical, and biological properties, and it is vital to understanding the 45 taxonomic and functional dynamics of microbiomes in amended soils in order to improve 46 the process performance. 47 Introduction 50Cadmium is characterized by its toxicity, accumulation, and mobility in the environment, 51 and can result in potential hazards for human health through the soil-food chain transfer 52 (1). In recent years, with the increases in atmospheric deposition and human activities, 53 such as mining, the application of organic and inorganic fertilizers or sewage sludge, and 54 wastewater irrigation, heavy metal pollution in soil has increased dramatically (2,3,4). In 55China, heavy metal pollution in soil is decreasing the country's grain harvest by tens of 56 millions of tons every year (5, 6). Another study showed that more than 70% of the rice 57 grain samples from metal-contaminated rice fields across south China were 58 Cd-contaminated (7). The multi-target regional geochemical survey of Chengdu 59 economic zone revealed that the abundance of heavy metals, especially cadmium, was 60 abnormal over large areas of Deyang (northeast of the Chengdu Plain). Besides, the 61 results of the ecological geochemical assessment conducted in this region showed that 62 the source of heavy metals pollution of soil, such as cadmium pollution, is the LongmenMountains, which accumulates the mineral cadmium and near-surface atmospheric dust 64 produced by industrial and mining enterprises. Heavy metal pollution has been a severe 65 challenge to the sustainable utilization of cultivated land resource and food production 66 safety. Therefore, environmental engineers have given high priority to the reduction of of 67 toxic metal bioavailability in croplands to ensure food security and human health (8). 68 At present, the techniques of soil heavy metal pollution remediation are divided into 69 four parts: phytoremediation, micro-remediation, physical remediation, and chemical 70 remediation. The new-soil technology, adsorption, and electrokinetics (EK) belong to the 71 physical remediation group, while leaching, biological reduction, complexation, and 72 in-situ immobilization (9) are all part of the chemical remediation group. Of these 73 remediation technologies, in-situ immobilization is considered to be the most effective 74 and low-cost remediation, especially for non-point source pollution in cultivated soil (10). 75The key to the technology is to select suitable amendments, of which the most commonly 76 used ones are alkaline materials, phosphorous materials, clay minerals, iron manganese 77 oxides and organic materials (11). These materials can change the existing forms of 78 heavy metal in soil through ion exchange, adsorption, and precipitation, and reduce the 79 mobility and bioavailability of heavy metals. The environmental effect ...