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Uptake and Photosynthetic Inhibition by Atrazine and its Degradation Products on Four Species of Submerged Vascular Plants¹

ABSTRACT

The photosynthetic inhibitory effect of atrazine (2-chloro-4-ethylamino-6-isopropyl amino-1,3,5-triazine) and three of its major metabolites (deethylated, deisopropylated, and hydroxyatrazine) were determined for four species of submerged macrophytes: Potamogeton perfoliatus L., Ruppia maritima L., Myriophyllum spicatum L., and Zannichellia palustris L. The four species showed a similar response to varied dosages of the parent atrazine compound with an average I₁ (concentration at which photosynthesis is inhibited by 1%) for the four species of 20 µg/L and an average I₅₀ (concentration at which photosynthesis is inhibited by 50%) for the four species of 95 µg/L. The three major degradation metabolites of atrazine produced varying degrees of photosynthetic inhibition in the four species, but generally the order of toxicity was deethylated > deisopropylated > hydroxyatrazine with hydroxyatrazine causing an apparent stimulation of photosynthesis in several species. Of four species tested, Myriophyllum spicatum L. was the most resistant to atrazine and its metabolites. The magnitude of the actual uptake of the compounds [µg compound/grams dry wt (gdw) plant] by the plants correlated closely with the photosynthetic inhibitory response, i.e., at the same concentration the uptake of atrazine > deethylated > deisopropylated > hydroxyatrazine. Considering that an extremely high environmental concentration (0.5 mg/L) of deethylated atrazine for an estuary only produced a photosynthetic inhibition of from 20 to 40% in four major species of submerged macrophytes, it is concluded that the degradation products of atrazine tested did not play a major role in the disappearance of the submerged vascular plants from the Chesapeake Bay.

Key Words: herbicide • metabolites • aquatic plants • estuarine • phytotoxic

¹ University of Maryland Center for Environ. and Estuarine Studies. Contribution no. 1480.

² Assistant Professor, Horn Point Environ. Labs., Cambridge, MD 21613; and Research Technician, Univ. of Maryland, Princess Ann, MD 21853.

Received for publication May 6, 1983.