A toxicity test for the effects of chemicals on the non-target submersed aquatic macrophyte, Myriophyllum sibiricum Komarov
A laboratory toxicity testing system with 'Myriophyllum sibiricum ' Komarov (northern watermilfoil) was developed for predicting the effects of pesticides and other phytotoxic chemicals upon non-target submersed macrophytes. Features of this toxicity test that enhance standardisation include a chemically defined medium, artificial sediment and inoculation of each tube with an axenic 'M. sibiricum' macrophyte segment. It is a static, partial life cycle laboratory toxicity test that determines the toxicant effect on plant growth over fourteen days. Endpoints measured included growth rate, plant height, root number and length, fresh and dry weight, plant area, oxygen production, change in membrane integrity, chlorophyll 'a', chlorophyll 'b' and carotenoid content. Once the toxicity testing. system was established, eight herbicides (atrazine, 2,4-D, diquat, fluridone, glyphosate, hexazinone, metolachlor and triclopyr) and two reference toxicants (ZnCl2 and phenol) were tested on the growth and development of 'Myriophyllum sibiricum'. The toxicity test successfully detected the toxic effects of the reference toxicants and the technical herbicides at their maximum label rates (MLR) as applied to water 15 cm in depth. Once the MLR was determined to be toxic, serial dilution tests were conducted to establish no observable effect levels (NOEL) and IC50s (concentration to inhibit the parameter by 50%). If stimulation was observed in the endpoint parameter, SC20s (concentration to stimulate the parameter by 20%) were calculated. Compared with the results from other aquatic plant species, 'M. sibiricum', as tested in this axenic toxicity test, was highly sensitive to the phytotoxic effects of 2,4-D, fluridone, glyphosate, triclopyr and phenol. This static, axenic toxicity test is a fast, simple and accurate method that can determine possible effects of new herbicides and other phytotoxic chemicals on non-target submersed macrophytes.