Zostera marina L. growth response to atrazine in root-rhizome and whole plant exposure experiments

Abstract

Atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino-]- s-triazine), a triazine herbicide, is one of the most widely used herbicides in the Chesapeake Bay watershed. Increased use of atrazine in the 1970s coincided with a decline in the abundance of Zostera marina L. (eelgrass). Ground-water surveys have found atrazine in concentrations that may affect eelgrass growth and survival. The effects of atrazine in groundwater discharges on the growth of eelgrass through root-rhizome exposure were examined in laboratory systems. A long term, dynamic, groundwater simulation study was conducted with atrazine concentrations ranging from 0.0 to 2.5 mg·l −1. No significant effects on chlorophyll content, growth or survival were detected. A static root-rhizome exposure experiment was conducted using split chamber exposure systems to verify these results, atrazine concentrations were increased by an order of magnitude. Neither mortality nor significant effects on plant growth were detected (maximum atrazine concentration 7.6 mg·l −1). A static, whole plant exposure experiment was conducted, and mortality was observed at atrazine concentrations of 1.9 mg·l −1 and above. This work suggests that eelgrass is not susceptible to atrazine through root-rhizome uptake, and that atrazine exposure via groundwater seepage did not cause the declines in eelgrass abundance and distribution.