The Mae Tao watershed, northwest Thailand, has become contaminated with cadmium (Cd) as a result of zinc ore extraction (Padaeng deposit) in the nearby Thanon-Thongchai mountains. Consumption of contaminated rice has led to documented human health impacts. The aim of this study was to elucidate transfer pathways from creek and canal waters to the paddy field soils near Baan Mae Tao Mai village and to determine the relationship between Cd speciation in the soil and uptake by rice plants. Transfer mainly occurred in association with particulate matter during flooding and channel dredging and, in contrast with many other studies, most of the soil Cd was associated with exchangeable and carbonate-bound fractions. Moreover, there was a linear relationship between soil total Cd and rice grain Cd (R(2) = 0.715), but a stronger relationship between both the Tessier-exchangeable soil Cd and the BCR-exchangeable soil Cd and rice grain Cd (R(2) = 0.898 and 0.862, respectively).

Cadmium (Cd) contaminated soils from the Mae Sot district in northwest Thailand, a region in which rice Cd concentrations often exceed health limits (0.4 mg/kg) set by the World Health Organisation, were examined for isotopically exchangeable Cd (Cd E values using a 111 Cd spike) to determine how this rates as a predictor of rice grain Cd in comparison with soil total Cd and solution extractable Cd (using the commonly applied BCR scheme and, in an attempt to distinguish carbonate bound forms, the Tessier soil sequential extraction scheme reagents). Step 1 of the BCR scheme (0.11 M CH3COOH) and step 1 of the Tessier scheme (1M MgCl2) showed the highest R 2 values in regressions with rice Cd (91% and 90%, respectively), but all predictors were strongly linked to rice Cd (p<0.001) and could be used for prediction purposes. One soil, of the six tested, was an exception to this, where all predictors overestimated grain Cd by a factor of 2.5 to 5.7, suggesting that rice grain Cd had been restricted here by the differing flooding regime and subsequent changes to redox conditions. E values and Tessier step 1 extractions were closely related, indicating that these measurements access similar pools of soil Cd. Separately, the isotopic exchangeability (representing bioavailability) of Cd was also assessed in two soils amended with rice husk and miscanthus biochars (0, 1, 5, 10, 15 and 20% w/w) in order to assess the utility of the biochars as a soil amendment for immobilising Cd in-situ. One soil showed significant reductions in Cd E value at 5% rice husk biochar addition and at 15% miscanthus biochar addition however, based on the E value-rice grain Cd regression relationship previously established, the E values in the amended soils still predicted for a rice Cd concentration above the health limit. In the second soil, neither of the biochars successfully reduced the Cd E value. This indicates that further work is needed to customise biochar properties to suit specific soil and contaminant situations if they are to be used successfully for remediation of metal contaminated soils.

This article describes a combination of the driver-pressure-state-impact-response (DPSIR) framework and the logical framework approach (LFA) to develop water management strategies for a lagoon floodplain in Thailand. The DPSIR framework identified the cause-effect relationship between water and anthropogenic activities. LFA developed management strategies based on a systematic and logical approach. DPSIR analysis for the issue of water shortages for irrigated areas revealed the need for income from agriculture is a major driver, as indicated by agricultural development policy. The driver exerted pressure on increasing irrigation water demand, which increased the risk of a water shortage. The impact of water shortage was indicated by loss of farmer income. Existing responses led to inadequate problem-solving, for example, the promotion of mixed farming. Using data captured from DPSIR analysis for LFA analysis, proposed strategies to address the root causes of “ineffective irrigation water allocation” focused on improving (1) the performance of rotating irrigation systems; (2) monitoring water allocation; and (3) water use efficiency. The strategies developed using the combined DPSIR framework and LFA are effective because: (1) this method provides insight into complex water systems; (2) the strategies are developed logically to solve the problem at its root cause; and (3) there is intensive stakeholder participation and in-depth study of the area. This method is a helpful tool for developing a management strategy for a complex water system and is suitable for application by decision-makers. Stakeholder verification is required for future research to ensure that the strategies are appropriate and capable of being implemented.