| Arsenic(As) is a naturally ubiquitous toxic metalloid. Generally, arsenic enters farmlands in the way of atmospheric deposition and wastewater discharging, and will threaten human health through the food chain. Arsenic aging is a natural process happened in soil. Studies on As aging will make great sense for the proper evaluation of As risk of releasing into soils and the rational utilization of As-contaminated soils. In this study, three types of soils derived from different parent materials were collected, including quaternary red clay(RS1), purple sandy shale(RS2) and granite(RS3). The aging process of different forms of exogenous As in soils and its impact factors, the influence of different organic acids on As aging in soils, and As phytoavailability after different aging period were studied by conducting pot and soil incubation experiments. The main results are summarized as follows:(1) The exogenous arsenite(As(III)) were totally transformed into arsenate(As(V)), while demethylation of dimethylarsinic acid(DMA) were formed in three types of soils after 120 d aging. DMA demethylation with As(V) as production was the dominant process in RS1 and RS3, of which the complete transformation periods were 120 d and 90 d, respectively. However, the monomethylarsonic acid(MMA) emerged accompanied with DMA demethylation in RS2, of which the complete transformation period was 120 d. The content of available As in RS2 was significantly higher than the other two soils throughout the aging period. Soil p H, organic matter(SOM), and the Fe, Al, and Mn oxides were the main factors influencing As(III) aging in soils. Comparatively, Mn oxides played a more crucial role than Fe and Al oxides in As aging. Amorphous Fe and Al oxides were the main factors influencing DMA aging in soils. During As(III) and DMA aging in soils, non-specifically sorbed As and specifically sorbed As gradually decreased with time, which means relatively stable As fractions, such as well-crystallized hydrous Fe/Al oxides associated As and residual As produced.(2) Under the conditions of 25 ℃, 70% of the maximum field moisture capacity and aerobic dark, Organic acid types had no significant effect on As aging in RS1. No significant variance was also observed for As fractionations in soils after adding organic acids, while organic acid amounts significantly affected the available As and As fractionations in soils. Acetic acid of 50 and 100 mg·kg-1 inhibited As aging in soils, while promotion was observed at 200 mg·kg-1 of acetic acid. At 50 mg·kg-1, oxalic acid and citric acid addition promoted the As aging, while the inhibition effect on As aging was obtained at 100 and 200 mg·kg-1. Adding humic acid inhibited the As aging, especially, a more crucial role in RS1 than others. At 50-200 mg·kg-1, acetic acid and oxalic acid addition had significant effects on the specifically sorbed As. Citric acid and hunic acid both at 50 and 100 mg·kg-1 presented significant effects on amorphous and poorly-crystalline hydrous Fe/Al oxides associated As. At 200 mg·kg-1, acetic acid, citric acid and hunic acid addition had significant effects on the well-crystalline hydrous Fe/Al oxides associated As.(3) The biomass of the rape gradually increased with the As aging in soils, while the As content by the rape shoot and root and the content of available As gradually decreased with the As aging. This result indicated that the aging time of As greatly affected phytoavailability of As in soils. For the same period of As aging, the rape biomass in three types of soils generally decreased in the order of RS1, RS3 and RS2. The contents of As by the rape shoot and root as well as the contents of available As gradually decreased in the same order of RS2, RS3 and RS1. This means that soil properties could significantly affect As phytoavailability and crop growth. For the different plant parts of the rape, the content of As by root was obviously higher than that in shoot. |
PDF Full Text Request