Table 1.
Summary of detected herbicides in the GBR and its catchment. Comparison of water quality guideline values (WQGVs)39 (all of low reliability) based on freshwater species and proposed water quality guideline values (PGVs)43,44,93 for 99%, 95%, 90% and 80% species protection (based on marine and freshwater species) against toxicity thresholds [no effect concentration (NEC); effect concentration inhibiting the specific growth rate by 10% (EC10))] values derived for Rhodomonas salina in this study (from Table 3). All concentrations in µg L−1. NA signifies no available guideline values. Bold indicates herbicides tested in this study.
| Herbicide | Mode of action | WQGVs | PGVs | Guideline reliability | NEC This study | EC10 This study | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PC99 | PC95 | PC90 | PC80 | PC99 | PC95 | PC90 | PC80 | |||||
| ‘Priority’ PSII inhibitor herbicides | ||||||||||||
| Diuron | Inhibition of photosynthesis at PSII | 0.2* | 0.43 | 0.67 | 0.86 | 1.2 | Very high | 1.7 | 1.9 | |||
| Hexazinone | 75* | 1.8 | 2.5 | 3.1 | 4 | Low | 4.6 | 4.0 | ||||
| Tebuthiuron | 0.02 | 2.2 | 20 | 160 | 4.7 | 11 | 17 | 26 | Moderate | 23 | 28 | |
| Ametryn | 0.5 | 1 | 1.6 | 0.10 | 0.61 | 1.3 | 2.8 | Low | ||||
| Atrazine | 0.7 | 13 | 45 | 150 | NA | NA | ||||||
| ‘Alternative’ PSII inhibitor herbicides | ||||||||||||
| Bromacil | Inhibition of photosynthesis at PSII | 180* | 0.23 | 1.1 | 2.2 | 4.8 | Moderate | 5.5 | 4.9 | |||
| Fluometuron | NA | 20 | 40 | 55 | 77 | Low | ||||||
| Metribuzin | NA | 2 | 2.7 | 3.1 | 3.9 | Moderate | 2.2 | 2.7 | ||||
| Terbuthylazine | NA | 0.40 | 0.97 | 1.6 | 2.8 | Moderate | ||||||
| Propazine | NA | 2.2 | 4.6 | 6.4 | 9.2 | Low | 28 | 42 | ||||
| Simazine | 0.2 | 3.2 | 11 | 35 | 28 | 63 | 84 | 130 | Low | 48 | 38 | |
| Terbutryn | NA | 0.079 | 0.26 | 0.51 | 1.2 | Moderate | ||||||
| Prometryn | NA | 0.11 | 0.52 | 1.1 | 2.2 | Low | ||||||
| ‘Alternative’ non-PSII inhibitor herbicides | ||||||||||||
| 2,4-D | Auxin mimic, promotes uncontrolled growth | 140 | 280 | 450 | 830 | 1,000 | 2,500 | 3,800 | 5,800 | Low | >279,000 | >279,000 |
| Fluroxypyr | NA | 87 | 200 | 290 | 440 | Low | ||||||
| MCPA | 1.4* | 1 | 17 | 60 | 240 | Low | ||||||
| Imazapic | Inhibition of AHAS | NA | 0.049 | 0.44 | 1.2 | 3.6 | Very low | 363,000 | 410,000 | |||
| Metsulfuron-methyl | NA | NA | NA | |||||||||
| Metolachlor | Inhibition of cell division | NA | NA | NA | ||||||||
| Haloxyfop | Inhibition of ACCase | NA | 590 | 2,000 | 3,400 | 590 | 2,000 | 3,400 | 6,100 | Low | >3,700 | >3,700 |
| Fluazifop | NA | NA | NA | |||||||||
*Level of protection unknown.