Castor cake has been used extensively around the world as one of the recommended organic fertilizers due to it has high nitrogen content and many active ingredients which could prevent plant diseases. Ricinine, a toxic alkaloid, is one of the active ingredients and may be released into the soil from castor cake. To date, however, there is limited information on the fate of ricinine in the soil-plant system after castor cake application. To understand whether ricinine will be released from the castor cake into soil followed by plant uptake, the present study first established optimized ricinine analytical methods in various matrices through solid-phase extraction (SPE) (for water samples) or modified QuEChERS (for castor cake, soil, and plant samples) both coupled with a liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS). The established method was then utilized for the test of ricinine residue in a loam soil applied with a commercially available castor cake (containing ricinine at 1093 mg kg-1) and in the soil pore water. Plant uptake of ricinine was also evaluated using a hydroponically grown lettuce. The instrument detection limit for ricinine through LC-QTOF/MS analysis could be as low as &lt;1 µg L-1, and the recoveries of ricinine in soil, soil pore water, and lettuce were all higher than 70% with relative standard deviations all &lt;20%. After 1, 7, and 14 days of castor cake application to the soil (in pots, 2 g castor cake per kg soil), ricinine was determined at levels of 1415.47, 1266.04, and 796.10 µg kg-1 in soil, and 257.16, 230.42, and 60.90 µg kg-1 in soil pore water, respectively. Results also showed that ricinine can be taken up by lettuce from water. After 3 days of lettuce uptake with nutrient solution containing 50 µg L-1 of ricinine, ricinine was determined in both lettuce shoots (58.00 µg kg-1, ww) and roots (26.41 µg kg-1, ww). The results obtained from this study using the established ricinine analytical methods indicate that after ricinine release from castor cake into soil pore water, it could be potentially taken up by plants, which may pose risk to human health after consuming ricinine contaminated crops. Therefore, further in-depth study of the ricinine transport and distribution in the soil-water-plant continuum under the typical practice of castor cake application is needed for accessing the risk of human and environmental health.

Impact of castor cake application on the fate of toxic alkaloid ricinine in soil

ACS Fall 2021

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