The purpose of this project is to clarify the routes of exposure to lead contamination in farmland food crops. The lead content in the air was measured and environmental media such as soil, water bodies, sediments, pesticides, and fertilizers were also sampled. In addition, stable lead isotope analysis, sequential extraction analysis, laser ablation inductively coupled plasma mass spectrometry, and statistical analysis methods were adopted to test environmental media and rice crops. Additionally, we explored the pathways of lead into food crops by investigating the factors influencing heavy metal uptake, establishing a model for assessing lead uptake in rice from paddy soil, and assessing the international regulatory soil standards for lead. Furthermore, a nationwide investigation plan for lead in farmland soil was formulated.
The results of foliar uptake experiment revealed that lead sources in both soil and foliage influenced lead uptake in the brown rice. In a saturated concentration of experimentally designed lead solution (PbSO4, 40 mg/L), the foliage accounted for the greatest uptake (45%). The results from the farmland experiment in the Tongancuo Section of Wuri District, Taichung indicated that under the influence of lead sources in both soil and air, the foliage uptake of lead was primarily from the air. The results indicated that the lead content in brown rice increased with decreased pH and increased sand content in soil. In summary, the analysis of lead in the plant tissues showed that, besides uptake by roots, foliar route is of similar importance to the soil-root pathway as a route of transport to the exposed parts of the plants.
In this project, the results also showed that the sum of soluble fraction, exchangeable fraction, and carbonate fraction from sequential extraction, DTPA extraction, and total lead content were all positively related to lead content in brown rice.
A predictive model and a discriminant model were established for assessing the uptake of lead in brown rice from paddy soil. Results of the modeling analysis showed similar results, i.e., the lead content in brown rice increased with increased lead concentration in soil and decreased pH, suggesting that the abovementioned factors may have caused contaminated brown rice in Tongancuo Section of Wuri District, Taichung.
The interpretation results of applying stable lead isotope analysis indicated that Tongancuo exhibited characteristics of farmland pollution. Rice crops that were cultivated on soil with high concentrations of lead displayed consistency in isotopic characteristics between each portion of the rice plants and the source of lead in the polluted soil. This indicates that the lead uptake from soil crucially influenced the increase in lead concentration in each portion of the rice plants. Thus, stable lead isotope analysis continues to be a vital tool for identifying sources of contamination.
This project examined the management and formulation bases or principles of farmland regulatory standards of the United States, Japan, the Netherlands, and Canada. In principle, the majority of regulatory standards were established based on risk assessments. The aforementioned data revealed that the general process of current international environmental management involves formulating corresponding standards based on factors such as health risk assessments, economic integration, and administrative considerations. Therefore, the findings of this study can be used as a crucial basis for Taiwan EPA in amending soil contamination regulatory standards.
In summary, lead uptake that occurred in brown rice can be partially attributed to lead content in the air. Future studies on cases of lead contamination in rice can consider procedures for monitoring lead concentration in the air in conjunction with related administrative units. Through a series of past projects, the EPA has gradually established multiple lead isotope detection techniques and analytical methods for environmental media. Conducting relevant projects to apply lead isotope analysis as a support tool for identifying environmental pollution and thereby promote its application is recommended.