Mercury in soil derived from igneous rock in Northern Kyushu, Japan

Abstract

Soil profiles with different vegetation, developed on igneous rock-derived areas in Northern Kyushu have been sampled at 13 locations and analyzed for total Hg with a flameless atomic absorption spectrometer. The associated parent rock was also analyzed. The Hg levels of each rock sample were too low, not exceeding 10 ppb, to exert a significant effect within the profiles on the total Hg content. The Hg content was generally higher in the soil than in the underlying rock, irrespective of the depth of the horizon. Surface enrichment of Hg was observed at most of the sample sites, some paddy fields in particular, resulting in steep concentration gradient down the profiles. The total Hg in all the surface horizons ranged from 459 to 64 ppb with a mean of 197 ppb. Obviously, mercurial application in recent years was a principal factor above all with regard to the establishment of the elevated Hg levels in the upper soil horizon under cultivation. Man-made loading of this element, probably through rain, was indicated even in the soils under natural vegetation, after taking into account a possible residual Hg concentration in the soil formation process. A close relationship in the profile distribution pattern between total Hg and organic matter contents was observed. This fact, in conjunction with the results of pyrolysis studies, did suggest that a large proportion of the total Hg in these soils could be firmly held by chemical forces, very likely as highly insoluble organic complexes.

Volcanic influence on mercury in soils of kagoshima, Southern Kyushu, Japan

“…As had been observed in similar soils elsewhere (9,30), accumulation in the surface horizons including Ao horizon was evident in most of the profiles under natural vegetation. Such a distribution was presumably due to recycling of the element by sucsive generation of plants with the ability of their roots to uptake Hg from the lower soil horizons.…”

“…Total Hg content of the soil averaged 40 ppb with a range between 3 and 245 ppb and had a median content of 26 ppb. These data are relatively at the lower bound of the range found in the soil derived from igneous rock in northern part of Kyushu where all of the soil horizons have a Hg content of 5 to 459 ppb with a mean of 80 ppb (9). It was remarkable that C horizons for most profiles had equally low values of less than 10 ppb which were among the lowest recorded in all the horizons.…”

“…The highest value, 245 ppb, was obtained from a paddy field, while accumulations in the upper horizons of upland and citrus orchard soils were considerably lower and had contents below 90 ppb. A major portion of the variation was undoubtedly derived from the past use of the land including mercurial applications for specific crops such as rice (8,9). Figs.…”

“…Varying amounts and types of humic material and clay in soil have been found co modify the ability of soil to accumulate Hg (8,9,12,29). The correlation coefficients relating total Hg to organic matter in the horizons for Gokabeppu and Fukuyama profiles were highly significant with r=0.624 and 0.628, respectively (p<O.OOI).…”

“…This study was therefore undertaken to provide an estimate of natural background Hg concentrations together with the degree and extent of suspected Hg contamination in the soil profiles in southern Kagoshima, representing diverse geological origin and pedological character under the volcanic activity. This work has been performed in conjunction with other studies on the Hg content of soils in Kyushu (8,9).…”