Kiyoshi Kurosawa

Groundwater–soil–crop relationship with respect to arsenic contamination in farming villages of Bangladesh – A preliminary study

To clarify the groundwater-soil-crop relationship with respect to arsenic (As) contamination, As concentration was measured in tubewell (TW) water, surface soil from farmyards and paddy fields, and fresh taro (Colocasia esculenta) leaves from farmyards in the farming villages of Bangladesh. The As concentration in TW water from farmyards was at least four times higher than the Bangladesh drinking water standard, and the concentration in fresh taro leaves was equal to or higher than those reported previously for leafy vegetables in Bangladesh. As concentration of surface soils in both farmyards and paddy fields was positively correlated with that of the TW water. Further, the concentration in surface soil was positively correlated with levels in fresh taro leaves in the farmyard. This study, therefore, clarified the groundwater-soil-crop relationship in farmyards and the relationship between groundwater-soil in paddy fields to assess the extent of As contamination in Bangladeshi villages.

Arsenic and heavy metal contamination in soils under different land use in an estuary in northern Vietnam

Heavy metal contamination of soil and sediment in estuaries warrants study because a healthy estuarine environment, including healthy soil, is important in order to achieve ecological balance and good aquaculture production. The Ba Lat estuary of the Red River is the largest estuary in northern Vietnam and is employed in various land uses. However, the heavy metal contamination of its soil has not yet been reported. The following research was conducted to clarify contamination levels, supply sources, and the effect of land use on heavy metal concentrations in the estuary. Soil samples were collected from the top soil layer of the estuary, and their arsenic (As), chromium (Cr), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) concentrations were analyzed, as were other soil properties. Most soils in the estuary were loam, silt loam, or sandy loam. The pH was neutral, and the cation exchange capacity ranged from 3.8 to 20 cmol·kg−1. Manganese and iron concentrations averaged 811 µg·g−1 and 1.79%, respectively. The magnitude of the soil heavy metal concentrations decreased in the order of Zn > Pb > Cr > Cu > As > Cd. The concentrations were higher in the riverbed and mangrove forest than in other land-use areas. Except for As, the mean heavy metal concentrations were lower than the permissible levels for agricultural soils in Vietnam. The principal component analyses suggested that soil As, Pb, Zn, Cd, and Cu were of anthropogenic origin, whereas Cr was of non-anthropogenic origin. The spatial distribution of concentration with land use indicated that mangrove forests play an important role in preventing the spread of heavy metals to other land uses and in maintaining the estuarine environment.

Variation in Arsenic Concentration Relative to Ammonium Nitrogen and Oxidation Reduction Potential in Surface and Groundwater

Abstract Arsenic (As), ammonium‐nitrogen (N), nitrate‐N concentrations, and oxidation–reduction potential (ORP) in the water samples from the river, pond, dug well, and shallow and deep tube wells (TW) were investigated in a farming village of southwestern Bangladesh. Concentrations of As and ammonium‐N were the highest, whereas ORP was the lowest in the shallow TW water among the water sources. The ammonium‐N concentration correlated positively with the As concentration and negatively with ORP for all samples, irrespective of the water sources. A rise in the ammonium‐N concentration was hypothesized to enhance microbial activity, which in turn would lower ORP, and then As was released from sediments to the surrounding water in a reducing condition. The source of ammonium‐N in the shallow TW water was identified as N fertilizer, based on the δ15N analysis. Thus, the influence of N fertilizer application on As contamination in groundwater was suggested.

Monitoring of Inorganic Nitrogen Levels in the Surface and Ground Water of the Red River Delta, Northern Vietnam

Abstract Concentrations of ammonium-nitrogen (N) and nitrate-N and the pH of the surface and ground water were monitored in three rural communes differing in topography, soil type, and cropping pattern in the central Red River Delta, northern Vietnam, at the end of the rainy season in 2002. Information on the amount of fertilizer N applied and the kind and number of livestock feeding was obtained through interviews of the farmers. The amount of fertilizer N annually applied by a farm household was around 400 kg/ha in average and was a very high level compared to other Asian countries. The ammonium-N concentrations of the surface and ground water were relatively high and exceeded the Vietnamese water standard for purposes other than drinking use and for drinking use, respectively. Possible impacts of the topography of the communes on the ammonium-N concentration of the surface were suggested. The nitrate-N concentrations of both surface and ground water were generally lower than 0.4 mg/L with an exceptionally high value of 5 mg/L in the grey degraded soil area, and were always below the ammonium-N concentrations at the corresponding sites in the alluvial soil area, indicating the suppressed condition of nitrification in the soil and water. The low pH of the ground water measured at some sites in the grey degraded soil area was out of the Vietnamese water standard for drinking use.

Temporal and Spatial Variations of Inorganic Nitrogen Levels in Surface and Groundwater Around Hanoi, Vietnam

Abstract Pollution of surface and groundwater by inorganic nitrogen (N) was assessed in farm villages of northern Vietnam. The pH and ammonium‐N and nitrate‐N concentrations were monitored at three communes near Ha Noi in the Red River Delta in March and September 2003, following monitoring in October 2002. In each monitoring time, ammonium‐N concentrations exceeded the Vietnamese water standards applicable to surface and groundwater, whereas the nitrate‐N concentrations were relatively low and below the corresponding standards. Neither spatial nor temporal variation was found in the ammonium‐N and nitrate‐N concentrations of the surface water. A temporal increase in the ammonium‐N concentration was statistically confirmed in the groundwater. Intensively applied fertilizer‐N and disposed animal/human wastes were thought to be sources of ammonium‐N. Ammonium‐N originating from those sources was seen to accumulate steadily in the groundwater through percolation from the surface water and surrounding land. A spatial variation of the nitrate‐N concentration was observed in the groundwater. The nitrate‐N concentration in the groundwater was particularly low in communes located in lowland areas with alluvial soils. The suppression of nitrification or promotion of denitrification was considered to be responsible for the low nitrate‐N concentration. A spatial variation was also found in the groundwater pH. Therefore, variation of the pH may be linked to variation of the nitrate‐N concentration in the groundwater.

Evaluation of the physical properties of water treatment residue for use as a soil substitute compared with decomposed granite soil

Abstract To evaluate water treatment residue (WTR) as a soil substitute material, its physical properties were investigated and compared with decomposed granite soil (DGS). For comparison purposes, relative gas diffusivity (D/D 0), saturated hydraulic conductivity (K s), water retention curve, porosity and readily available water were measured for both the WTR and the DGS. The measured D/D 0, K s, water retention ability and porosity were higher for the WTR than for the DGS. These differences may be attributable to intra-aggregate and inter-aggregate pores created in the WTR through binding of silt and clay particles in the flocculation process. The behavior of water and gasses surrounding these pores may explain the physical properties of the WTR. The characteristics measured in this evaluation indicate that WTR has good potential for reuse as a soil substitute material.

Heavy Metal Contamination of Irrigation Water, Soil, and Vegetables in a Multi-industry District of Bangladesh

Heavy metal (Cr, Cu, Zn, As, Cd, and Pb) concentrations in irrigation water, soil, and vegetables were measured to assess the contamination levels in a multi-industry district in Bangladesh. In this district, wastewater discharged from three industrial areas (textile, dye, agrochemical, paint and ceramics factories) was mixed with irrigation water. The Zn, Cu, Pb, and Cr concentrations were high in both irrigation water and soil, and all of these concentrations exceeded the permissible limits except for the Cd and Pb concentrations in irrigation water. Hierarchical cluster analysis of the irrigation water and soil data revealed that the contamination of irrigation water and soil was caused by the discharge of industrial waste into the irrigation water. The heavy metal concentrations in leafy vegetables were mostly below the FAO permissible limits, whereas the As, Cr, and Pb concentrations in root vegetables exceeded the permissible limits. Correlation and cluster analyses of the vegetable data showed that the use of contaminated irrigation water and soil might be responsible for the heavy metal contamination in vegetables. According to the bioconcentration factor (BCF) in root vegetables, the transfer from soil to vegetables of As, Cr, Zn, and Pb was moderate/low, whereas that of Cd and Cu was high. Since these root vegetables were deemed unsafe for human consumption, this type of contamination should be considered more seriously when planting root vegetables.

Contamination of Agricultural Soils by Toxic Trace Metals in an Industrial District in Vietnam

Contamination of agricultural soils by toxic trace metals of arsenic (As), lead (Pb), cadmium (Cd), chromium (Cr), copper (Cu) and zinc (Zn) was investigated in an industrial district in Vietnam. In the district, irrigation agriculture is performed through channels, in addition, there are two industrial parks are nearby agricultural land. The purpose of the study is to clarify the magnitude and spatial distribution of the trace metal concentrations, the source of the trace metals, the difference in the concentrations between the two industrial park areas, and usability of soils for agriculture. As a result, the trace metal concentrations were in the order of Cr>Zn>Pb>Cu>As>Cd for the district. No significant differences were observed between the two park areas in concentrations. Cr and Zn concentrations were high near factories in the park areas, and the other concentrations were comparatively high in the areas, showing that the trace metals were supplied from the factories with wastewaters. The correlations observed between Cd, Pb and Zn, between Cr and Zn, and between Cu and as in the concentrations suggested that there were several groups of wastewaters supplying the trace metals. Concentrations of all kinds trace metals exceeded the permissible level for agricultural soils, and the remediation measures to reduce contamination are necessary.

Arsenic Speciation and Extraction and the Significance of Biodegradable Acid on Arsenic Removal—An Approach for Remediation of Arsenic-Contaminated Soil

A series of arsenic remediation tests were conducted using a washing method with biodegradable organic acids, including oxalic, citric and ascorbic acids. Approximately 80% of the arsenic in one sample was removed under the effect of the ascorbic and oxalic acid combination, which was roughly twice higher than the effectiveness of the ascorbic and citric acid combination under the same conditions. The soils treated using biodegradable acids had low remaining concentrations of arsenic that are primarily contained in the crystalline iron oxides and organic matter fractions. The close correlation between extracted arsenic and extracted iron/aluminum suggested that arsenic was removed via the dissolution of Fe/Al oxides in soils. The fractionation of arsenic in four contaminated soils was investigated using a modified sequential extraction method. Regarding fractionation, we found that most of the soil contained high proportions of arsenic (As) in exchangeable fractions with phosphorus, amorphous oxides, and crystalline iron oxides, while a small amount of the arsenic fraction was organic matter-bound. This study indicated that biodegradable organic acids can be considered as a means for arsenic-contaminated soil remediation.

Physicochemical Properties of Plant Growing Medium Comprising Water Treatment Residuals Amended with Composted Park

The physicochemical properties were measured for medium comprising water treatment residuals (WTR) amended with composted bark (two different volume ratios of WTR to composted bark) one month after creation, in order to determine its suitability for plant growing purposes. Compared to the WTR alone, the WTR + bark medium exhibited similar neutral pH and a redox potential (Eh) indicating aerobic conditions, higher electrical conductivity (EC), cation exchange capacity (CEC), and total carbon (C) and nitrogen (N) concentrations, and lower phosphate (P) absorption coefficients and available manganese (Mn) concentrations. Comparing to the theoretical baseline medium immediately after creation, the WTR + bark medium, after a one-month incubation, exhibited a decline in available Mn, total C, and total N concentrations and an increase in CEC and P-absorption coefficients. These changes may be attributable not only to the introduction of