Additive toxicity of herbicide mixtures and comparative sensitivity of tropical benthic microalgae.
Natural waters often contain complex mixtures of unknown contaminants potentially posing a threat to marine communities through chemical interactions. Here, acute effects of the photosystem II-inhibiting herbicides diuron, tebuthiuron, atrazine, simazine, and hexazinone, herbicide breakdown products (desethyl-atrazine (DEA) and 3,4-dichloroaniline (3,4-DCA)) and binary mixtures, were investigated using three tropical benthic microalgae; Navicula sp. and Cylindrotheca closterium (Ochrophyta) and Nephroselmis pyriformis (Chlorophyta), and one standard test species, Phaeodactylum tricornutum (Ochrophyta), in a high-throughput Maxi-Imaging-PAM bioassay (Maxi-IPAM). The order of toxicity was; diuron > hexazinone > tebuthiuron > atrazine > simazine > DEA > 3,4-DCA for all species. The tropical green alga N. pyriformis was up to 10-fold more sensitive than the diatoms tested here and reported for coral symbionts, and is recommended as a standard tropical test species for future research. All binary mixtures exhibited additive toxicity, and the use of herbicide equivalents (HEq) is therefore recommended in order to incorporate total-maximum-load measures for environmental regulatory purposes.
Magnusson
Marie
M
AIMS@JCU, Australian Institute of Marine Science, James Cook University, Townsville, QLD 4811, Australia.
Heimann
Kirsten
K
Quayle
Pamela
P
Negri
Andrew P
AP
D001681:Biological Assay; D000460:Chlorophyta; D017377:Diatoms; D058735:Environmental Policy; D006540:Herbicides / Q000633:toxicity*; D014329:Tropical Climate; D014874:Water Pollutants, Chemical / Q000633:toxicity*
D006540:Herbicides; D014874:Water Pollutants, Chemical