The relative sensitivity of macrophyte and algal species to herbicides and fungicides: An analysis using species sensitivity distributions

Abstract

Lemna spp. are the standard test species representing aquatic macrophytes in the current risk assessment schemes for herbicides and plant growth regulators in the European Union and North America. At a Society of Environmental Toxicology and Chemistry (SETAC) 2008 workshop on Aquatic Macrophyte Risk Assessment for Pesticides (AMRAP), a Species Sensitivity Distribution (SSD) working group was formed to address uncertainties about the sensitivity of Lemna spp. relative to other aquatic macrophyte species. For 11 herbicides and 3 fungicides for which relevant and reliable data were found for at least 6 macrophyte species, SSDs were fitted using lognormal regression. The positions of L. gibba (the most commonly tested Lemna species) and Myriophyllum spicatum (for which standardized test methods are under development) in each SSD were determined where data were available. The sensitivity of standard algal test species required for pesticide registration in the United States under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) relative to the macrophytes in each SSD was also examined (algae were not included in the SSD). L. gibba was among the most sensitive macrophyte species for approximately 50% of the chemicals examined. M. spicatum was among the most sensitive macrophytes for approximately 25% of the chemicals. In most cases, the lowest FIFRA algal species endpoint was lower than the most sensitive macrophyte endpoint. Although no single species consistently represented the most sensitive aquatic plant species, for 12 of 14 chemicals L. gibba and the FIFRA algae included an endpoint near or below the 5th percentile of the macrophyte SSD. For the other compounds, M. spicatum was the most sensitive species of all aquatic plants considered. Integr Environ Assess Manag 2013;9:308-318. © 2012 SETAC

Guidance on tiered risk assessment for plant protection products for aquatic organisms in edge‐of‐field surface waters

“…The PPR Panel suggests, as a pragmatic approach, to perform a test on a dicot macrophyte when terrestrial dicot species are more than a factor of 10 more sensitive than monocot terrestrial species. Following the results of the SSD analysis reported in the paper by Giddings et al (2013), Myriophyllum spicatum should be a preferable dicot species to test additionally. The AMRAP document (Maltby et al, 2010) recommends the use of growth rate endpoints for macrophytes.…”

“…An analysis using SSDs by Giddings et al (2013) indicated that neither Lemna gibba nor Myriophyllum spicatum is consistently among the most sensitive macrophyte species for all the herbicides and fungicides included in their analysis. The L. gibba EC 50 is within a factor of 10 of the HC 5 of the macrophyte SSD for 6 of 11 chemicals investigated, indicating that RA based on Lemna 31 If in one or more of the screening or efficacy tests with vascular plant species showing 50 phytotoxic effects at the maximum recommended application rate (MRR) or higher, the a.s. is considered to have herbicidal activity (see EPPO scheme for higher plants (EPPO, 2003)).…”

“…algae and macrophytes). The AMRAP document (Maltby et al, 2010) and Giddings et al (2013) provide guidance on the use of macrophyte toxicity data in the SSD approach and define areas of uncertainty which are specifically associated with the selection of species and endpoints. The uncertainty associated with species and endpoint selection to assess toxicity for algae is generally less because of the availability of standard protocols that are already used for a fairly long time.…”

Is the tier‐1 effect assessment for herbicides protective for aquatic algae and vascular plant communities?

“…Species sensitivity distributions integrate the results of laboratory toxicity experiments with a least 8 species to estimate hazardous concentrations (HC x values) for a given fraction of species [9]. Microcosm and mesocosm studies represent tier 3 of the risk assessment [1].…”

Scientific Opinion on good modelling practice in the context of mechanistic effect models for risk assessment of plant protection products

“…photosynthesis inhibitors), algae and macrophyte data may have a similar sensitivity. However, herbicides that inhibit amino acid synthesis and herbicides with an auxin simulation mode of action generally seem to be more toxic to aquatic vascular plants than to algae (Giddings et al, 2013). Currently, knowledge of the MOA of several other types of herbicides is limited.…”