chlorophyll-a and hexazinone

Herbicides are often detected in watersheds at concentrations that are toxic to phytoplankton, potentially causing indirect effects on higher trophic organisms. The long-term effects of 5 applications over 30 d of binary mixtures of the herbicides diuron and hexazinone were assessed at "low" and "high" concentrations typically found in the environment, using mesocosms. Sixteen of 95 phytoplankton taxa, 3 of 18 zooplankton taxa, and 6 of 14 macroinvertebrate taxa responded negatively to contaminant exposures. Herbicide applications altered the phytoplankton community structure. Relative abundance of Cyanophyceae decreased following 5 applications from 52.1% in the control to 37.3% in the low treatment and to 25.9% in the high treatment, while Chlorophyceae increased to 50.6% in the low treatment and to 61.7% in the high treatment compared with the control (39.7%). Chlorophyceae had the greatest number of affected species (8), whereas 1 species within the Cyanophyceae was negatively affected on more than 1 sampling day. Further, chlorophyll a was reduced on 4 and 5 d out of the 8 total sampling days in the low and high treatments, respectively, compared with the control. These results highlight that integrating multiple taxa and contaminants with long-term exposures in ecological risk assessments of herbicides can facilitate the ability to make predictive and mechanistic generalizations about the role of herbicides in shaping patterns of species abundance in natural systems. Environ Toxicol Chem 2017;36:2234-2244. © 2017 SETAC.

Topics: Amphipoda; Animals; Aquatic Organisms; Chlorophyll; Chlorophyll A; Diuron; Environmental Monitoring; Herbicides; Phytoplankton; Triazines; Water Pollutants, Chemical; Zooplankton

Recently a new Maxi-Imaging-PAM (Max-I-PAM) instrument for phytotoxicity assessment via chlorophyll fluorescence imaging was introduced. This new instrument allows rapid detection of the effects of PS II inhibiting herbicides which are high use agricultural chemicals frequently detected in surface waters in Australia and elsewhere. Several studies have applied the new instrument for detection of phytotoxicants in water using microalgae suspensions; however, these use preliminary protocols and to date no validated method is available for high throughput testing of environmental samples in 96-well plates. Here we developed and applied a new protocol allowing dose-response assessment of four samples within 2 h (8 dilutions in duplicate). The technique was found to be sensitive, with a detection limit of 2.3 ng l(-1) for the herbicide diuron when testing solid phase extracts (SPE) of 1000 ml water samples, and reproducible both between experiments (coefficient of variation (CV)=0.30) and within the 96-well plate (CV=0.06). Relative potencies were determined for four reference PS II impacting herbicides (diuron>hexazinone>atrazine>simazine). Extracts from 1000 ml environmental samples and diuron spiked ultrapure water as well as passive sampler extracts were evaluated and good agreement was found between diuron equivalent concentrations calculated from bioassay results (DEQ(IPAM)) and DEQ(CHEM) values calculated from LCMS chemical analysis of the four reference compounds in the same samples. Overall, the technique provides a valuable bioanalytical tool for rapid and inexpensive effects-based assessment of PS II impacting herbicides in environmental mixtures.

Topics: Atrazine; Australia; Biological Assay; Chlorophyll; Diuron; Dose-Response Relationship, Drug; Fresh Water; Herbicides; Image Enhancement; Microscopy, Fluorescence; Photosystem II Protein Complex; Reproducibility of Results; Risk Assessment; Sensitivity and Specificity; Simazine; Triazines; Water Pollutants, Chemical

Topics: Atrazine; Cell Division; Chlorophyll; Chlorophyta; Cyanobacteria; Dose-Response Relationship, Drug; Fluorometry; Herbicides; Spectrophotometry; Time Factors; Triazines