Spatial variability of soil selenium as affected by geologic and pedogenic processes and its effect on ecosystem and human health

Abstract

Selenium (Se) deficiency and excess in agricultural ecosystems are related to many human health problems through the food chain and depend on the spatial variability and bioavailability of Se in soils. This paper examines the spatial variability of Se in soils as affected by geologic and pedogenic processes and its effects on rice grains, groundwater, and human health using Rugao County, Jiangsu Province, an agricultural area in Yangtze River Delta Region, which has a high level of nonagenarians, as a case study. The results showed that total soil Se (T-Se) concentration in the study area (average 0.13 ± 0.02 mg kg -1 , n = 203) was close to the Se Clark value, the Se mean concentration in earth crust, and had narrow spatial variation as a result of consistent geological processes. As a fraction of the potential bio-available Se in ecosystems, soil water soluble Se (WS-Se) (average 2.27 ± 1.09 µg kg -1 , n = 203) had wide spatial variation. The higher concentrations of WS-Se were spatially distributed on loamy and highly weathered soils in the east and north of the county. Spatial heterogeneity of WS-Se was primarily due to changes in soil physicochemical properties caused by pedogenic processes related to cultivation. Average Se concentration in the rice grains and groundwater were 97 ± 69 µg kg -1 (n = 93) and 0.19 ± 0.21 µg L -1 (n = 95), respectively. Similar spatial variability and correlation between WS-Se and rice Se, groundwater Se, and longevity ratio (an index of nonagenarians per 100,000 inhabitants), were found, indicating that the soluble fractions of Se in soils play an important role in biogeochemical cycling in the ecosystem and might be an important indicator of Se deficiency or excess in soils. Thorough small-scale surveys of element availability in the soil should be emphasized where geologic settings are simple but pedogenic processes are complex due to intensive human activities. So WS-Se in soils was advised as a better indicator for Se environmental effect than T-Se, especially when dealing with simple geologic settings and complex pedogenic processes on a small scale.

Relationships among Environment, Climate, and Longevity in China

“…This is because Se varied largely even at a small scale in soil, high Se content and low Se content usually coexist in a city, and the research scale of this paper is still too large to show relationship between Se and longevity. Some studies at the town scale and county scale within a city have shown that climate factors is almost the same, so Se will be more significant related to longevity [ 24 , 25 , 26 , 27 , 28 ].…”

“…Soil Se can be considered as total Se (T-Se) and water-soluble (WS) Se (WS-Se). Soil WS-Se is a better indicator of environmental effects than T-Se [ 28 ]. In this study, both T-Se and WS-Se content of soil were considered.…”

Selenium in the Soil-Plant Environment: A Review

“…In soils with low Se concentrations (<2 mg kg -1 ), the relationship between total and bioavailable selenium was roughly linear whereas in soils with total Se more than 2 mg kg -1 , there was no relationship between total and bioavailable selenium [27]. Water soluble Se is a better indicator of Se deficiency or toxicity than total Se in the soil [107]. Total concentrations do not give an adequate representation of environmental impact of Se because of its partitioning on solid phases within the soil.…”

Selenium Partitioning and Stable Isotope Ratios in Urban Topsoils

“…The occurrence of different chemical Se species in soil is related to pH, redox potential, and other soil solution properties including ionic strength and concentration of dissolved organic matter controlled by soil mineralogy and soil microbial activities. The water-soluble fractions of Se in soils play an important role in the biogeochemical cycling of Se in ecosystems and are the best indicators of Se deficiency or excess in soils (Sun et al, 2009). The oxidized forms of Se, selenate Se( VI), and selenite/hydroselenite Se(IV), are water soluble and hence more mobile and bioavailable.…”