Eight species of plants were exposed to nitrobenzene in a hydroponic solution. Four species experienced no depression of either transpiration or photosynthetic rates, while one was rapidly killed and the other three were temporarily affected but recovered from the treatment. Uptake of nitrobenzene was passive and was shown to be proportional to the rate of water flux in each species. The transpiration stream concentration factor (TSCF) was 0.72. The root concentration factor (RCF) was variable between the species and was higher than expected, presumably due to deposits of insoluble metabolic products. All of the species examined displayed a capacity to chemically alter nonpolar nitrobenzene into both polar and insoluble products. Volatilization of nitrobenzene from the leaves was a major route of chemical loss.
A five-day, whole plant toxicity test was developed and evaluated. The 18 chemicals tested were primarily substituted benzenes and phenols, although representative herbicides, surfactants, and other industrial chemicals were also tested. The test yields information on root and shoot growth as a function of toxic chemical concentration in the root environment and can also be used to determine the effect on transpiration. The measurement found to be the most sensitive indicator of toxicity was total plant growth. EC50 (effective concentration that reduced growth 50%) values were estimated for each compound using regression analysis. This simple bioassay gives a quick response to an acute exposure and can be used to screen chemicals at various concentrations. The beginning of a unique database comparing species, concentrations, and chemical toxicity are presented, and the results are discussed in relation to other phytotoxicity data.
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