Impacts of land use/cover and slope on the spatial distribution and ecological risk of trace metals in soils affected by smelting emissions

The soil contamination around smelting sites shows high spatial heterogeneity. This study investigated the impacts of distance, land use/cover types, land slopes, wind direction, and soil properties on the distribution and ecological risk of trace metals in the soil around a copper smelter. The results demonstrated that the average concentrations of As, Cd, Cu, Pb, and Zn were 248.0, 16.8, 502.4, 885.6, and 250.2 g mg kg-1, respectively, higher than their background values. The hotspots of trace metals were primarily distributed in the soil of smelting production areas, runoff pollution areas, and areas in the dominant wind direction. The concentrations of trace metals decreased with the distance to the smelting production area. An exponential decay regression revealed that, depending on the metal species, the influence distances of smelting emissions on trace metals in soil ranged from 450 to 1000 m. Land use/cover types and land slopes significantly affected trace element concentrations in the soil around the smelter. High concentrations of trace metals were observed in farmland, grassland, and flatland areas. The average concentrations of trace metals in the soil decreased in the order of flat land > gentle slope > steep slope. Soil pH values were significantly positively correlated with Cd, Cu, Pb, Zn, and As, and SOM was significantly positively correlated with Cd, Pb, and Zn in the soil. Trace metals in the soil of the study area posed a significant ecological risk. The primary factors influencing the distribution of ecological risk, as determined by the Ctree analysis, were land slope, soil pH, and distance to the source. These results can support the rapid identification of high-risk sites and facilitate risk prevention and control around smelting sites.

Association between hilliness and walking speed in community-dwelling older Japanese adults: A cross-sectional study

PURPOSE

This cross-sectional study investigated the association between hilliness and walking speed in community-dwelling older adults, and whether it varied according to their car-driving status.

METHODS

Data were collected from 590 participants aged 65 and older living in Okinoshima Town, Shimane prefecture, Japan, in 2018. Comfortable walking speed (m/s) was objectively assessed. Hilliness was measured by the mean land slope (degree) within a 500-m or 1000-m network buffer around each participant's home using a geographic information system. A multiple linear regression examined whether the land slope was associated with walking speed, adjusted for sex, age, body mass index, smoking habits, alcohol consumption habits, exercise habits, chronic disease, and living arrangements. A stratified analysis by car-driving status was also conducted.

RESULTS

After adjusting for all confounders, the land slope within the 500-m or 1000-m network buffer was negatively associated with walking speed (B = -0.007, 95% CI [-0.011, -0.002]; B = -0.007, 95% CI [-0.011, -0.003], respectively). The stratified analysis by car-driving status showed that living in a hilly area was negatively associated with walking speed among non-drivers in the 500-m or 1000-m network buffer (B = -0.011, 95% CI [-0.017, -0.004]; B = -0.012, 95% CI [-0.019, -0.006]), though there were no associations among drivers.

CONCLUSIONS

A hilly environment is positively associated with slow walking speed in community-dwelling older adults in Japan. Moreover, car-driving status potentially modifies the relationship between living in a hilly environment and slow walking speed.

Decay and erosion-related transport of sulfur compounds in soils of rubber based agroforestry

Elemental sulfur is intensively used to control weeds and rubber leaf diseases. However, the mechanisms contributing to elemental sulfur dissipation and decay (hereafter decay) in rubber agroforestry remains unclear. This study relates hydrological processes such as runoff and soil loss to the changes in soil total sulfur (S_tot) and sulfate (S-SO₄) in typical hillslope rubber agroforestry intercropped with cocoa in Xishuangbanna. The elemental sulfur decay kinetics were studied at two slopes (top and bottom) and three agrosystems (weed, no-weed and mixed). The results show that soil moisture and hydraulic conductivity was uniformly distributed in the experimental rubber agroforestry settings. Higher soil loss and runoff occurred in the bottom slope than the top slope, and in no-weed agrosystem than the herbaceous agrosystems (weed and mixed). The soil loss was mainly driven by runoff. Moreover, S_tot and S-SO₄ in runoff water were higher in weed agrosystem than no-weed agrosystems. Soil S_tot best fit a two-compartments kinetics model, with lower kinetic rates in elemental sulfur applied treatments than in the no-added elemental sulfur treatments, particularly for the weed agrosystem. The soil S_tot dissipation time 50% (DT₅₀) was 10-14 times higher in top slope than bottom slope; but 4 and 20 times higher in mixed and no-weed agrosystems, respectively, compared to the weed agrosystem. The soil S_tot and S-SO₄ contents negatively correlated with soil microbial respiration (CO₂ efflux), indicating an adverse influence of elemental sulfur on soil microbial activity. In short, elemental sulfur decay and its S-SO₄ transformation depended on soil moisture, runoff, soil erosion and soil CO₂, which are in turn affected by slope and agrosystem. This study not only clarifies the mechanisms of elemental sulfur dissipation and decay for its use as an environmental friendly agrochemical; but it also provides information to understand the contribution of runoff and soil loss on these mechanisms in rubber agroforestry.