Production of chlorinated hydrocarbons and methyl iodide by the red microalga Porphyridium purpureum

Two experiments were performed using axenic batch cultures of the red microalga Porphyridium purpureum . The cultures were grown in sealed 5‐liter glass vessels under a high‐purity artificial atmosphere and analyzed for the production of several halocarbons, including chloroform (CHCl 3 ), methylene chloride (CH 2 Cl 2 ), methyl iodide (CH 3 l), trichloroethylene (C 2 HCl 3 ), and tetrachloroethylene (C 2 Cl 4 ). Two cultures and a control were used in each experiment. The first experiment followed the system for 17 d at low light intensity (20 μmol quanta m −2 s −1 ), while the second was comprised of 7 d at low light followed by 24 h at high light intensity (800 umol quanta m −2 s −1 ). In both experiments, only chloroform and methyl iodide were produced in measurable quantities. This is the first report of chloroform production in a microalgal species. The chlorophyll a (Chl a) normalized production rate of chloroform in the various cultures ranged between 1.3 × 10 −7 and 7.8 × 10 −7 mol (g Chl a) −1 d −1 (15–93 μg [g Chl a] −1 d −1 ). Chloroform production peaked during the logarithmic growth phase. Methyl iodide production ranged between 2.0 × 10 −7 and 1.2 × 10 −6 mol (g Chl a ) −1 d −1 (28‐170 μg [g Chl a ] −1 d −1 ). Exposure of the cultures to high irradiance (800 μmol quanta m −2 s −1 ) did not stimulate the production of any of the compounds. In contrast to an earlier published account involving this species of algae, the production of tri and tetrachloroethylene was not detected in any of the cultures under either low or high irradiance.