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Phytotoxicity in Bush Bean of Five Sulfur-Containing Gases Released from Advanced Fossil Energy Technologies¹

ABSTRACT

Sulfur-containing gases including sulfur dioxide (SO₂), hydrogen sulfide (H₂S), carbon disulfide (CS₂), carbonyl sulfide (COS), and methyl mercaptan (CH₃SH) are a major class of atmospheric emissions from advanced fossil energy technologies. Although phytotoxicity data for SO₂ and H₂S exist, the influence on vegetation of the remaining S gases is not known. This study was designed to address the comparative toxicity of the five gases in bush bean (Phaseolus vulgaris). Seedlings were exposed to each gas individually for 6 hr at a range of concentrations (6–82 µmol m^–3) in an open gaseous exchange system, during which whole-plant net photosynthesis and transpiration were monitored. At the highest exposure levels, leaf necrosis was assessed 3 d after exposure. Transpiration did not respond consistently to any of the treatments. Neither CS₂ nor CH₃SH caused any change in photosynthesis or foliar necrosis. Based on the inhibition of photosynthesis and the development of leaf necrosis at equivalent volumetric concentrations in the atmosphere, the toxicity of the remaining three gases was SO₂ > H₂S > COS. The relationship between net photosynthesis and exposure dosage (concentration x time) for H₂S, SO₂, and COS was curvilinear and biphasic, exhibiting in each gas an enhancement of photosynthesis followed by inhibition as the dosage increased. For projected emission rates from advanced fossil energy facilities, the results suggest that releases of CH₃SH and CS₂ are not likely to influence vegetation. Since plant response to H₂S, SO₂, and COS is strongly dosage dependent, accurate estimates of field effects due to these three gases must await more adequate air quality modeling near commercial-scale facilities.

Key Words: sulfur dioxide • hydrogen sulfide • carbonyl sulfide • carbon disulfide • methyl mercaptan • hormesis

¹ Research sponsored by the Office of Health and Environ. Res., U.S. Dep. of Energy, under contract W-7405 eng-26 with Union Carbide Corp. Publication no. 2251, Environ. Sci. Div., Oak Ridge Natl. Lab., Oak Ridge, TN 37830.

² Research Staff Member and Senior Lab. Technician, respectively, Environ. Sci. Div., Oak Ridge Natl. Lab.

Received for publication August 5, 1982.