Quantifying ricin in agricultural soils
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To date there are no reports of extensive scientific investigations on the analysis, determination or content of ricin, RCAeo (Ricinus communis agglutinin - 60 kDa) in agricultural soils. To accurately quantify the amount of ricin available within the soil, a modified ELISA (Enzyme Linked Immunosorption Assay) was developed. The ELISA followed an extraction process using an isotonic saline solution as a ricin carrier. The range of ricin detection was between 0.010 ^g ricin/g soil to 0.300 |jg ricin/g soil as contrasted with the previously employed radial immunodiffusion assays with a sensitivity limited tol.O mg ricin/gram soil. Using the modified ELISA method, the ricin content in the surrounding soil of germinating castor seeds planted 0.5 cm deep in 25 g of soil was detennined in Olton and Amarillo soils. These two soils are common agricultural soils in Lubbock, Texas area. Ricin was detected in both soils washed off the seeds of germination days four, six and eight days after seeding. Ricin was not detected in days two or ten after seeding. In addition, ricin was not found in any of the remaining soil. An investigation quantifying ricin within a field (30 meters by 152 meters) that had supported a crop of castor (Ricinus communis) in a previous growing season with an intermediate crop of cotton (Gossypium hirsutum), ricin was detected. In a separate field study, ricin was also only detected during the last December sampling of the same year crop. Soil in this study was the Amarillo fine sandy loam. Half of a castor field (121 meters by 121 meters) had been pivot irrigated. The other half had been furrow irrigated. Ricin detected was significantly less in the furrow irrigated half when compared to the center pivot irrigation. Ricin was also noted in response to a controlled stress trial only when the stress consisted of a combination of saline irrigation water EC (Electroconductivity) of 10 dS/m and drought. No other stresses, such as heat (35.0 °C to 38 °C), saline irrigation or drought, alone resulted in any detectable ricin within the sampled the soil. This data suggests that a combination of growth conditions combined with a specific set of external stress factors and human cultivation methods may play a determining role in the natural deposition ricin in agricultural soil as well as its long-term retention.