Light induced degradation of phorbol esters

Jatropha curcas (Jatropha) is a tropical shrub that is gaining popularity as a biofuel feedstock plant. Phorbol esters (PEs) are tetracyclic tiglian diterpenoids that are present in Jatropha seeds and other parts of plant. Epidermal cell irritating and cancer promoting PEs not only reduce commercial values of Jatropha seed cake but also cause some safety and environment concerns on PE leaching to soil. A simple bioassay of PE toxicity was conducted by incubating 48 h old brine shrimp (Artemia salina) nauplii with Jatropha oil for 24 h. 1–4% of Jatropha oil (corresponding to PE concentration of 25–100 mg L−1) had mortality rate of 5–95%, with LC50 estimated to be 2.7% of oil or 67 mg L−1 of PE. Jatropha oil was incubated with clay or black soil (autoclaved or non-autoclaved) in the darkness or under sunlight for different periods of time before oil was re-extracted and tested for PE content by HPLC and for remaining toxicity with the brine shrimp bioassay. Under sunlight, PE decreased to non-detectable level within six days. Toxicity reduced to less than 5% mortality rate that is comparable to rapeseed oil control within the same period. In contrast, PE level and toxicity remained little changed when Jatropha oil was incubated in the darkness. Such PE degradation/detoxification was also found independent of the presence of soil or soil microorganisms. We conclude that sunlight directly degrades and detoxifies PEs and this finding should alleviate the concern on long term environmental impact of PE leaching.

► Phorbol esters in Jatropha curcas raise safety and environmental concerns. ► A simple, robust and sensitive test was used to monitor biotoxicity for PE with brine shrimp nauplii. ► The Bioassay and HPLC together were used to monitor PE toxicity and quantity in Jatropha oil. ► Sunlight effectively degrades and detoxifies PE, independent of soil or microorganism. ► This finding addresses the concern on long term environmental impact by possible PE leaching.