The investigation of the content of heavy metals (HMs) of soil was started from the 71st year, the survey on large district, middle district, intensive and bulk, etc. was continued over than 20 years. The HMs polluted (the content up to five grades deducts Cu, Zn) of Taiwan rice land was 319 hectares. Changhua county is mainly polluted area and account for 56% pollute. This object is directed irrigation water and sediments of rice land. In order to prevent the irrigating water or sediments contaminate, the main work item is collect rice land environmental database, understand HMs flow and distribute on rice land environment, discussion the sampling methods getting suitable. At first, the electronic database of rice land and irrigation ditch will construct, which includes the rice land, irritation ditch, paddy soil quality, domestic and international relevant research, relevant regulations of rice land contaminate and detection method, arranging the discharge household have priority to check the list to collect. The sampling method of HMs content of rice land will investigate. The sampling method to probe into the opportunity of sampling differently, ex. contaminate source to survey, regular monitor method, meticulous survey before renovation, to assay after renovation, it propose sampling method is with sampling purpose and opportunity to some principle. The schemes of prevention of rice land heavy metal contaminate monitoring will draft the tactics of the passive form propose regarding setting up the soil monitoring station, the active tactics are to cutting down the total amount of pollute. To emend removal of sediments administration guide, to collect relevant decree, is it removal of sediments the executive, principle and prospectus. Utilize the geographic information system (GIS) to probe into the rice land HMs to pollute, will be reference materials that list and manage enterprise organization by the environmental protection administration and discharge household by the Taiwan joint irrigation association, to screen the preliminary preferential contaminate list that checked of the suggestion, there are 779 data. The first 25% contaminate, who export getting heavy, account for 89% of total contaminate. After discharging the abolish water total amount on the potential risk analysis of rice land soil, the rice land could be separated to high , middle and low contaminated degree area. The high, middle and low contaminated degree area will monitor preferentially. This plan sampling adopt the systematic and grid sampling, period of it more collects to be different (generally and torrential rain) last irrigation channel water and sediments experimental analysis result the HMs in soils decrease in the directions of depth and distance from the irrigation entrance. The concentrations of HMs in irrigation water are extremely low as compared with those in suspended particles and sediments. The results suggest that the transports of HMs in irrigation ditch or in soils are possible in the forms of solid phases. Tessier sequential extractions of soils and sediments indicate that HMs are mainly associated with Fe/Mn oxides; however, HMs in each extracted fraction change with various samples and sampling locations, a possible result of dissociation and association of HMs with soil particles during HMs transfer. Take chromium metal as an example, a predication of HMs accumulations in soils was conducted through mass-balance calculation. The calculation leads to a result that it takes 54-607 years to re-contaminate reclaimed soils if HMs-bearing irrigation water and sediments are contributive factor to the accumulation of HMs in soils, obviously shorter than irrigating water is the only contributive factor; Irrigate water and sediments the specific gravity that pollute to the rice land HMs were 0.8-25.0% and 75.0-99.2% respectively. Can learn the rice land HMs pollutes the transmission that comes from the solid state particle by the above result, solid state particle to come from irrigation water suspend particle and sediment is it lead to the fact to suspend to erode. One of the objectives of this study was to investigate the health risk for human exposure to HMs contained in particulate matter (PM) emitted from the resuspension of the dry sediment after clean-up process and cost of sediments clearance policy in the irrigation ditch. Results obtained from the risk assessment indicated that the cancer risk of human exposure to dry sediment resuspension may exceed the acceptable cancer risk level (10-5-10-6) and possibility exists that non-cancer health effects; results show that the Cost-Benefit (BC) ratios in Taoyuan, Chunghua and Kaohsiung counties are all higher than one. The Irrigation system HMs contaminate for main transmission way, sediment is it works for move directly to remove except that contaminate sources best method. In order to stop the transmission of the contaminate sources, Irrigation system in the technology and method of system management, short period (in medium, high risk area to investigate a Intensive survey), middle period (cut down not irritating ditch total amount), long-term (Irrigation and drain off water system will be separating), consider in order to offer the administrative organization in light of actual conditions.

Farmland Heavy Metal contaminate; irrigation water quality; Sediments; Transport