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Chinampas are island plots (500-1000 m²) constructed of soil scooped from the bottom of the lake and surrounded by canals. Over 40 agricultural species, including vegetables, cereals, and flowers, are produced on chinampas and consumed by approximately 100,000 people. This agro-ecosystem, once one of the most diverse and productive, at present is at risk of disappearing, mainly as a consequence of the severe pollution of the irrigation water. To evaluate the relationship between the accumulation of metals and physical soil properties, total trace metals Fe, Cu, Mn and Zn and total heavy metals Pb, Ni, and Cr in soils were determined by Particle Induced X-Ray Emission (PIXE). This method provides a very suitable technique for treating a large number of samples because sample preparation is simple and determination of a large number of elements is simultaneous. Three sites were chosen because of their long history of pollution: Xochimilco, San Luis Tlaxialtemalco and Mixquic in Mexico City. Soil properties were determined by conventional analytical methods. Soils were found to be high in organic matter content, high in sodicity and salinity, and with an alkaline pH. The metals present in the samples are in the following order of abundance: Fe>Mn>Cr>Zn>Cu>Pb.

A PIXE (Proton Induced X-ray Emission) analysis is applied for measuring the concentration of 21 major and minor trace metal elements (in the range of Z=13-53) for normal, adenoma and carcinoma human thyroid tissues. A 2.0 MeV proton beam was employed to excite the samples. The thyroid samples were obtained from 14 patients during surgical operations, with which normal and damaged parts are concerned as an aid to understand the mechanisms of formation of thyroid cancer and as a complementary diagnostic tool. Thirty samples were measured in total. Fourteen samples of them were in pairs, i.e.14 tumor samples with 14 corresponding healthy tissue specimens taken at a distance from the tumor. The statistical analysis of the results shows the lower levels of the mean value of iron and iodine in the carcinoma tissues than those in the normal tissues; especially iodine is about one tenth of the normal value. On the contrary, the elevation of the mean value for calcium and zinc in the carcinoma tissues in comparison with the normal ones is observed, while in the adenoma tissues copper is very lower than those in the normal thyroid. The concentration of iron in the adenoma is two times of normal tissues.