Australian Institute of Marine Science, Townsville, QLD, 4810, Australia.
Queensland Alliance for Environmental Health Sciences (QAEHS), The University of Queensland, Woolloongabba, QLD, 4102, Australia.
Sci Rep. 2020 Nov 11;10(1):19592. doi: 10.1038/s41598-020-76363-0.
Conventional photosystem II (PSII) herbicides applied in agriculture can pose significant environmental risks to aquatic environments. In response to the frequent detection of these herbicides in the Great Barrier Reef (GBR) catchment area, transitions towards 'alternative' herbicides are now widely supported. However, water quality guideline values (WQGVs) for alternative herbicides are lacking and their potential ecological impacts on tropical marine species are generally unknown. To improve our understanding of the risks posed by some of these alternative herbicides on marine species under tropical conditions, we tested the effects of four herbicides on the widely distributed diatom Chaetoceros muelleri. The PSII herbicides diuron, propazine, and tebuthiuron induced substantial reductions in both 24 h effective quantum yields (ΔF/F') and 3-day specific growth rates (SGR). The effect concentrations, which reduced ΔF/F' by 50% (EC), ranged from 4.25 µg L diuron to 48.6 µg L propazine, while the ECs for SGR were on average threefold higher, ranging from 12.4 µg L diuron to 187 µg L tebuthiuron. Our results clearly demonstrated that inhibition of ΔF/F' in PSII is directly linked to reduced growth (R = 0.95) in this species, further supporting application of ΔF/F' inhibition as a valid bioindicator of ecological relevance for PSII herbicides that could contribute to deriving future WQGVs. In contrast, SGR and ΔF/F' of C. muelleri were nonresponsive to the non-PSII herbicide haloxyfop at the highest concentration tested (4570 µg L), suggesting haloxyfop does not pose a risk to C. muelleri. The toxicity thresholds (e.g. no effect concentrations; NECs) identified in this study will contribute to the derivation of high-reliability marine WQGVs for some alternative herbicides detected in GBR waters and support future assessments of the cumulative risks of complex herbicide mixtures commonly detected in coastal waters.
农业中使用的传统光系统 II（PSII）除草剂会对水生环境造成重大的环境风险。鉴于这些除草剂在大堡礁（GBR）集水区频繁被检出，现在广泛支持向“替代”除草剂过渡。然而，替代除草剂的水质指导值（WQGV）缺乏，它们对热带海洋物种的潜在生态影响通常未知。为了提高我们对一些替代除草剂在热带条件下对海洋物种造成的风险的认识，我们测试了四种除草剂对广泛分布的硅藻角毛藻的影响。PSII 除草剂敌草隆、丙草胺和特丁津都导致了 24 小时有效量子产量（ΔF/F'）和 3 天特定生长率（SGR）的显著降低。降低 ΔF/F' 50%的效应浓度（EC）范围为 4.25µg L 敌草隆至 48.6µg L 丙草胺，而 SGR 的 EC 平均高出三倍，范围为 12.4µg L 敌草隆至 187µg L 特丁津。我们的结果清楚地表明，PSII 中 ΔF/F'的抑制与该物种生长的降低（R=0.95）直接相关，这进一步支持将 ΔF/F'抑制作为 PSII 除草剂的有效生态相关性生物标志物的应用，这可能有助于推导出未来的 WQGV。相比之下，在测试的最高浓度（4570µg L）下，非 PSII 除草剂草除灵对 C. muelleri 的 SGR 和 ΔF/F'没有反应，这表明草除灵对 C. muelleri 没有风险。本研究中确定的毒性阈值（例如无效应浓度；NEC）将有助于推导出一些在 GBR 水域中检测到的替代除草剂的高可靠性海洋 WQGV，并支持未来对沿海水域中经常检测到的复杂除草剂混合物的累积风险的评估。
