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Transpiration Effect on the Uptake and Distribution of Bromacil, Nitrobenzene, and Phenol in Soybean Plants¹

ABSTRACT

The influence of transpiration rate on the uptake and translocation of two industrial waste compounds, phenol and nitrobenzene, and one pesticide, 5-bromo-3-sec-butyl-6-methyluracil (bromacil), was examined. Carbon-14 moieties of each compound were provided separately in hydroponic solution to mature soybean plants [Glycine max (L.) Merr. dwarf cultivar Fiskeby v] maintained under three humidity conditions. The uptake of each compound was determined by monitoring the removal of ¹⁴C from the hydroponic solution. The extent to which ¹⁴C was adsorbed to roots and translocated to plant shoots and leaves was examined by assaying root and shoot parts for ¹⁴C. Bromacil was taken up slower than the other chemicals, had the most ¹⁴C translocated to the shoot, and the amount translocated to the shoot responded directly to the rate of transpiration. In contrast, both phenol and nitrobenzene were rapidly lost from solution and bound to the roots. Less than 1.5% of the ¹⁴C from phenol or nitrobenzene was translocated to the plant shoots. Increased transpiration rates had little influence on root binding of ¹⁴C; however, increasing transpiration rate from low to medium was associated with an increased uptake of nitrobenzene. The three chemicals studied have similar Log K_ow values, but their interactions with soybean were not the same. Thus, despite the usefulness of the octanol/water partitioning coefficient in predicting the fate of organic chemicals in animals and in correlating with root binding and plant uptake for many pesticides, log K_ow may not be equally useful in describing uptake and binding of nonpesticide chemicals in plants.

Key Words: Organic chemical uptake • Plant uptake • Glycine max (L.) Merr. • Partitioning coefficient of octanol/water

¹ Contribution form the USEPA, Toxics and Pesticides Branch, Corvallis Environ. Res. Lab., Corvallis, OR 97333.

² Plant physiologists, USEPA, Toxics and Pesticide Branch, Corvallis, OR 97333; and Plant physiologist, Univ. of Oklahoma, Dep. of Botany and Microbiology, Norman, OK 73019.

Received for publication February 11, 1987.