Sensitivity of macrophyte-dominated freshwater microcosms to chronic levels of the herbicide linuron. I. Primary producers.

Effects of chronic concentrations of linuron (0, 0.5, 5, 15, 50, and 150 micrograms/L) were studied in indoor, macrophyte dominated, freshwater microcosms. The concentrations were kept at a constant level for 4 weeks. This paper is the first in a series of two and summarizes the course of the linuron concentrations in time and its effects on macrophytes, periphyton, and phytoplankton. These endpoints were studied from 3 weeks before the start of the treatment until 11 weeks after the start. The degradation of linuron in the water was lower at higher treatment levels, probably due to a decrease in pH. Linuron treatment resulted in a decrease in biomass of the macrophyte Elodea nuttallii and a clear decrease in abundance of the algae Cocconeis, Chroomonas, and Phormidium foveolarum. It was found that Cocconeis first decreased in biovolume and after 2 weeks also in abundance. The alga Chlamydomonas increased in abundance at the two highest doses, resulting in higher chlorophyll-a levels. The NOECs of 0.5 micrograms/L for the inhibition of the growth and photosynthesis of Elodea nuttallii, the abundance of Cocconeis and Chroomonas, and the oxygen and pH levels were the lowest recorded in the microcosms. The safety factors adopted by the EU in the Uniform Principles appeared to ensure adequate protection for the ecosystem in the case of chronic exposure to linuron.