Optimizing conditions for the use of chlorophyll derivatives for photodynamic control of parasites in aquatic ecosystems.

Recently, it was demonstrated that mosquito larvae can be killed by means of photodynamic processes after the larvae have incorporated the photosensitizer chlorophyllin or pheophorbid, and were treated with light. The water-soluble substances were applied to and incorporated by the larvae in darkness. With Chaoborus sp. a dark incubation of about 3 h is sufficient to yield mortality of about 90% and ≥6 h resulted in almost 100% mortality during subsequent illumination. Temperature did not influence mortality of the larvae significantly in a treatment of 6 h dark incubation and subsequent 3 h illumination. At 10°C, 20°C, or 30°C, between 80% and 100% of the treated larvae died when the light intensity from a solar simulator was above 30 W/m(2). Lower irradiances were less effective. The LD(50) value of magnesium chlorophyllin was about 22.25 mg/l and for Zn chlorophyll 17.53 mg/l, while Cu chlorophyll (LD(50) 0.1 mg/l) was shown to be toxic also without light. Chlorophyllin, which was lyophilized immediately after extraction, was far more lethal to the larvae (LD(50) 14.88 mg/l) than air-dried Mg chlorophyllin.