Triazine herbicides contribute to erosion of UK salt marshes

Recent research has shown that triazine herbicides at the sub-lethal concentrations found in Essex salt marshes may be contributing to salt marsh erosion. 

Salt marshes play a vital role in protecting the coastline: wave and tidal energy is reduced as seawater crosses the marshes. In their absence coastal defences must often be constructed or strengthened, at considerable expense.
    Most of Britain’s 40,000 acres of salt marsh are located in the south east of the country and have been in severe decline since the late 1950s largely, it was thought, because of rising sea levels. However, new research by Professor Chris Mason of Essex University points to another factor impacting salt marshes. Significant concentrations of herbicides have been detected in Essex salt marshes. These concentrations can be two orders of magnitude higher than those in the surrounding water indicating that residues may be accumulating in them. The most commonly used herbicides are the triazines, simazine and atrazine, which account for almost 40% of total herbicide use in Europe. Noting that the timing of the salt marsh decline coincided with the introduction of widespread herbicide use Professor Mason set about investigating the impact of triazine herbicides on salt marsh stability.
    At least two factors are known to stabilise salt marshes. Strong plants with extensive root systems lend more stability than weaker plants. In addition, unicellular algae called diatoms present in salt marshes produce a biofilm of large molecules thought to contribute to marsh stability by binding sediment particles together. In laboratory and field studies Professor Mason and his colleagues found that triazine herbicides at the sub-lethal concentrations often present in salt marshes both decreased the growth rate of salt marsh plants and of diatoms.
    The health of these salt marshes is of strategic importance in flood prevention in the south-east and as water levels continue to rise their importance will only increase. In addition, they contribute to native biodiversity with a number of plants and animals uniquely adapted to this environment.
    The safety of simazine and atrazine is being considered in the first stage of the European review of agricultural chemicals. No decision has yet been made as to whether they will be included. (RM)

Mason CF, Underwood GJC, Baker NR, Davey PA, Davidson I, Hanlon A, Long SP, Oxborough K, Paterson DM and Watson A, The role of herbicides in the erosion of salt marshes in eastern England, Environmental Pollution, 122: 41-49, 2003.

[This article first appeared in Pesticides News No. 61, September 2003, page 26]