Search

Diphenylarsinic acid, phenylarsonic acid, methylphenylarsinic acid (MPAA), dimethylphenylarsine oxide (DMPAO), and methyldiphenylarsine oxide (MDPAO) in soil and rice were extracted, separated by reversed-phase chromatography, and quantified by ICPMS with a membrane desolvating system. For the extraction of arsenicals from rice grain and straw, 68% HN[O.sub.3] provided better extraction efficiency than water, 50% methanol, or 2.0 mol L 1 trifluoroacefic acid. For the extraction from soil, 68% HN[O.sub.3] provided better extraction efficiency than [H.sub.2]O, 1 mol [L.sup.-1] [H.sub.3]P[O.sub.4], or 1 mol [L.sup.-1] NaOH. The contaminated soil contained all five aromatic arsenicals along with inorganic arsenicals as main species (5.86 [+ or -] 0.19 [micro]g of As [kg.sup.-1]: 60.8 [+ or -] 2.0% of total extracted As). After pot experiments, rice straw contained mainly DMPAO (7.71 [+ or -] 0.48 [micro]g of AS [kg.sup.-1]: 60.5 [+ or -] 3.7%), MDPAO (0.91 [+ or -] 0.07 pg of AS [kg.sup.-1]:7.2 [+ or -] 0.5%), and inorganic As (2.85 [+ or -] 0.20 [micro]g of As [kg.sup.-1]: 22.3 [+ or -] 1.6%). On the other hand, rice grain contained mainly MPAA (1.17 [+ or -] 0.04 [micro]g of AS [kg.sup.-1]: 86.7 [+ or -] 2.7%). The root uptake of each species from the soil and transport from straw to grains were significantly related to the calculated log [K.sub.ow] values.

Abstract: Stream terraces are geomorphic markers that can be used to gauge surface deformation in response to tectonic uplift. The surface deposits of the terraces form a chronosequence that indicates the rate and process of soil development. Placing a time or age constraint upon soil development has become one of the most important factors in the disciplines of soil science and fluvial geomorphology. The radiocarbon (14C) method is unable to date old terraces or soils, but the longer half-life of cosmogenic beryllium-10 (10Be) permits this isotope to be useful to determine soil ages and rates of formation. Red soils (redder than 7.5YR) are commonly distributed on old, high altitude stream terraces throughout Taiwan. In this study, three pedons of alluvium-related red soils were sampled from the Taoyang (TY-YM), Pakua (PK-1), and Chiayi terraces (CY-1), respectively located in northern, central, and southern Taiwan. According to field morphology and chemical analyses, these red soils are characterized in Soil Taxonomy as being highly weathered, and they are classified as Typic Hapludox (TY-YM and PK-1), and Typic Paleudult (CY-1). Meteoric 10Be dating shows ages of ⩾261ka for TY-YM, ⩾124ka for PK-1, and ⩾386ka for CY-1. However, the trend of these ages does not agree with the degree of soil development. The former two ages are likely underestimated through loss of 10Be due to strong leaching and considerable erosion. The age obtained from CY-1 may represent the required time for soils develop into oxisols in Taiwan. [Copyright &y& Elsevier]

14C ages and δ13C were examined for sclerotium grains to elucidate the characteristics of these grains distributed in forest soils. The ages of the grains from surface A horizons and buried A horizons were ca 100–200 bp and ca 300–1,200 bp, respectively. In comparison with humic acid extracts, the 14C ages were in the increasing order: humic acid fraction < humic acid Pg fraction < sclerotium grains. The δ13C values for sclerotium grains in surface A horizons and buried A horizons were approximately −31‰ to −28‰, and these values were approximately 2–4‰ smaller than those of humic acids and soils. The C content of the grains had a tendency to decrease with increasing 14C ages, while the C content of humic acid was constant with age. The 14C ages of sclerotium grains indicate the individual age of grain formation, which are more likely to assign closer ages to the beginning of soil forming than the 14C ages of humic acid. The low δ13C values for sclerotium grains have presumably originated from characteristically biological organics, which may be protected from attack in soils because of their structure. [ABSTRACT FROM AUTHOR]

(pp. 119–124) [ABSTRACT FROM AUTHOR]

Abstract: To provide information on the dynamics of inorganic carbon in the soil environment, vertical distributions of the Δ14C values of pedogenic carbonate were measured in Mongolian steppe soils under a vegetation sequence. Soil samples were taken from five sites in a forest steppe, steppe and govi steppe. Δ14C values for pedogenic carbonate at all sites ranged from −392‰ to −776‰. There were remarkable differences in vertical distributions of inorganic carbon contents and Δ14C values between the forest and govi steppe sites. In the forest steppe and steppe sites where inorganic carbon was not present in the A horizons, the vertical distribution of Δ14C values varied widely with depth. On the other hand, soils in the govi steppe contained inorganic carbon throughout the whole soil profile, and the Δ14C value decreased regularly with depth. In addition, soil pH and organic carbon and total nitrogen contents showed differences among the vegetation zones. From comparison of results from samples of forest steppe and steppe sites to those from govi steppe sites, it was found that vegetation and the soil chemical environment have a great effect on Δ14C values. [Copyright &y& Elsevier]