SEGH Articles

Cadmium (Cd) contamination of paddy fields in Mao Tao, Western Thailand

01 September 2011
Peerapat Kosolsaksakul is a 2nd year PhD student who was winner of the Springer / Hemphill Best Poster presentation at SEGH 2011.

 

My PhD research is in its second year at the University of Edinburgh studying the Geochemical Behaviour of Cd in a Contaminated Watershed, Tak Province, Western Thailand.

During the 1960-70s, major projects to develop chemically supported agriculture, infrastructure, industrial estates and mining were launched in order to enhance the Thai economy. Unfortunately, in the areas where these projects took place, this has led to ecosystem and, in some cases, human health deterioration. Over the last decade in particular, there has been an increasing number of biogeochemical studies which aim to provide a better understanding of the changes occurring within the ecosystem, especially in lowland areas which have been contaminated to a high level with potentially toxic heavy elements such as cadmium (Cd). 

One example of such a contaminated area is Mae Tao, a small watershed in Tak province, western Thailand.  In 2003, the International Water Management Institute in collaboration with the Department of Agriculture, Thailand, observed that the concentration of Cd in paddy fields and rice was more than a hundred times the common background values of 0.14 mg kg-1 and 0.2 mg kg-1 for soil and rice, respectively (Simmons, 2005). This caused great concern amongst farmers and local people not only due to the tangible health problems but also to the economic effects, e.g. decreased rice demand and a government policy of not supporting rice growing in these areas. This was particularly hard-hitting since Mae Tao watershed is one of the most suitable areas of land in Thailand (and the wider region) for rice farming, having fertile soils, a good water supply due to high annual rainfall and an appropriate irrigation system with plenty of small creeks and irrigation canals. The high quality of Mae Tao Jasmine rice had also previously been recognised by its attainment of premium grade runner-up in the national rice product awards in 2002. Following confirmation of the Cd contamination in this area, many government departments and university researchers were asked to characterise the nature and extent of heavy metals contamination and to suggest remedial action. To date, only one plan has been accepted by the Thai government; that is to replace paddy fields with bio-energy crops such as sugarcane and oil palm. Many local farmers are, however, reluctant to grow such crops for various reasons including uneasiness about being disconnected from food production.

Consequently, the question arises; is it possible to maintain the Mao Tao paddy fields without causing any impact on human health? In this project, one set of check-dams, canals and a group of 18 paddy fields near the Mao Tao creek were selected to study the geochemical behavior of Cd as it is transported from the creek to fields. Our initial results have confirmed that high concentrations of Cd are present in some of the paddy field soils with the highest values (up to ~88 mg kg-1) being obtained for fields furthest from the main creek. These fields were also the most low-lying and it was established from interviews with the field owners that the 0-25 cm topsoil had been transported from the fields nearest the irrigation creek to the lowest lying fields for water management reasons. Consequently, this may account for the high concentrations of Cd now present in the fields furthest from the creek.

Having established the extent and location of the contamination, it is important to assess its availability to the rice plants as this will have a major influence on the potential impact on human health. Initial experiments have involved the use of sequential chemical extractions to estimate bioavailable Cd in these neutral-basic soils. In moderately contaminated fields, Cd in the exchangeable fraction (extracted by MgCl2 at pH 7) ranged from ~22-45% and that bound to the carbonate fraction (extracted by CH3COONa at pH 4.5) ranged from ~45-72%. In the most heavily Cd-contaminated soils, the proportion in the exchangeable fraction was extremely high (over 70%) and it is predicted that rice grown in these fields will have Cd concentrations in excess of the safe level of 0.2 mg kg‑1.

Following quantification of Cd concentrations in the roots, shoots, husks and rice grain from each of the 18 paddy fields, further work will investigate the key factors controlling uptake of Cd by rice. The overall aim is to find a remedial approach that will minimise transfer of Cd from the soil to the rice grain and that can be readily implemented in Thailand.

 The Mao Tao region is only one example of an ecosystem affected by development activities; it should be viewed, however, as an important case study for developers and regulators to learn from in terms of potential impacts on ecosystems, community food sources and human health.

Peerapat Kosolsaksakul, Margaret C. Graham and John G. Farmer, School of GeoSciences,, University of Edinburgh, EH9 3JJ, UK.

Reference

Simmons, R.W., Pongsakul, P., Saiyasitpanich, D., Klinhoklap. S. Elevated levels of cadmium and zinc in paddy soils and elevated levels of cadmium in rice downstream of a zinc mineralized area in Thailand: implications for public health. Environmental Geochemistry and Health (2005) 27: 501-511.

 

Keep up to date

SEGH Events

Submit Content

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

Science in the News

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

  • Assessment of the toxicity of silicon nanooxide in relation to various components of the agroecosystem under the conditions of the model experiment 2018-08-18

    Abstract

    Investigation of SiO2 nanoparticles (NPs) effect on Eisenia fetida showed no toxic effect of the metal at a concentration of 250, 500 and 1000 mg per kg of soil, but conversely, a biomass increase from 23.5 to 29.5% (at the protein level decrease from 60 to 80%). The reaction of the earthworm organism fermentative system was expressed in the decrease in the level of superoxide dismutase (SOD) on the 14th day and in the increase in its activity to 27% on the 28th day. The catalase level (CAT) showed low activity at average element concentrations and increase by 39.4% at a dose of 1000 mg/kg. Depression of malonic dialdehyde (MDA) was established at average concentrations of 11.2% and level increase up to 9.1% at a dose of 1000 mg/kg with the prolongation of the effect up to 87.5% after 28-day exposure. The change in the microbiocenosis of the earthworm intestine was manifested by a decrease in the number of ammonifiers (by 42.01–78.9%), as well as in the number of amylolytic microorganisms (by 31.7–65.8%). When the dose of SiO2 NPs increased from 100 to 1000 mg/kg, the number of Azotobacter increased (by 8.2–22.2%), while the number of cellulose-destroying microorganisms decreased to 71.4% at a maximum dose of 1000 mg/kg. The effect of SiO2 NPs on Triticum aestivum L. was noted in the form of a slight suppression of seed germination (no more than 25%), an increase in the length of roots and aerial organs which generally resulted in an increase in plant biomass. Assessing the soil microorganisms’ complex during introduction of metal into the germination medium of Triticum aestivum L., there was noted a decrease in the ammonifiers number (by 4.7–67.6%) with a maximum value at a dose of 1000 mg/kg. The number of microorganisms using mineral nitrogen decreased by 29.5–69.5% with a simultaneous increase in the number at a dose of 50 mg/kg (+ 20%). Depending on NP dose, there was an inhibition of the microscopic fungi development by 18.1–72.7% and an increase in the number of cellulose-destroying microorganisms. For all variants of the experiment, the activity of soil enzymes of the hydrolase and oxidoreductase classes was decreased.

  • Seasonal characteristics of chemical compositions and sources identification of PM 2.5 in Zhuhai, China 2018-08-16

    Abstract

    Fine particulate matter is associated with adverse health effects, but exactly which characteristics of PM2.5 are responsible for this is still widely debated. We evaluated seasonal dynamics of the composition and chemical characteristics of PM2.5 in Zhuhai, China. PM2.5 characteristics at five selected sites within Zhuhai city were analyzed. Sampling began on January 10, 2015, and was conducted for 1 year. The ambient mass concentration, carbon content (organic and elemental carbon, OC and EC), level of inorganic ions, and major chemical composition of PM2.5 were also determined. Average concentrations of PM2.5 were lower than the National Ambient Air Quality Standard (NAAQS) 24-h average of 65 μg/m3. The daily PM2.5 concentration in Zhuhai city exhibited clear seasonal dynamics, with higher daily PM2.5 concentrations in autumn and winter than in spring and summer. Carbon species (OC and EC) and water-soluble ions were the primary components of the PM2.5 fraction of particles. Apart from OC and EC, chemical species in PM2.5 were mainly composed of NH4+ and SO42−. There was a marked difference between the summer and winter periods: the concentrations of OC and EC in winter were roughly 3.4 and 4.0 times than those in summer, while NH4+, SO42−, NO3, and Na+ were 3.2, 4.5, 28.0, and 5.7 times higher in winter than those in summer, respectively. The results of chemical analysis were consistent with three sources dominating PM2.5: coal combustion, biomass burning, and vehicle exhaust; road dust and construction; and from reaction of HCl and HNO3 with NH3 to form NH4Cl and NH4NO3. However, additional work is needed to improve the mass balance and to obtain the source profiles necessary to use these data for source apportionment.

  • Estimates of potential childhood lead exposure from contaminated soil using the USEPA IEUBK model in Melbourne, Australia 2018-08-14

    Abstract

    Soils in inner city areas internationally and in Australia have been contaminated with lead (Pb) primarily from past emissions of Pb in petrol, deteriorating exterior Pb-based paints and from industry. Children can be exposed to Pb in soil dust through ingestion and inhalation leading to elevated blood lead levels (BLLs). Currently, the contribution of soil Pb to the spatial distribution of children’s BLLs is unknown in the Melbourne metropolitan area. In this study, children’s potential BLLs were estimated from surface soil (0–2 cm) samples collected at 250 locations across the Melbourne metropolitan area using the United States Environmental Protection Agency (USEPA) Integrated Exposure Uptake Biokinetic (IEUBK) model. A dataset of 250 surface soil Pb concentrations indicate that soil Pb concentrations are highly variable but are generally elevated in the central and western portions of the Melbourne metropolitan area. The mean, median and geometric soil Pb concentrations were 193, 110 and 108 mg/kg, respectively. Approximately 20 and 4% of the soil samples exceeded the Australian HIL-A residential and HIL-C recreational soil Pb guidelines of 300 and 600 mg/kg, respectively. The IEUBK model predicted a geometric mean BLL of 2.5 ± 2.1 µg/dL (range: 1.3–22.5 µg/dL) in a hypothetical 24-month-old child with BLLs exceeding 5 and 10 µg/dL at 11.6 and 0.8% of the sampling locations, respectively. This study suggests children’s exposure to Pb contaminated surface soil could potentially be associated with low-level BLLs in some locations in the Melbourne metropolitan area.