Variation, Replication, and Power Analysis of Myriophyllum Spp. Microcosm Toxicity Data

Abstract

Myriophyllum spp. have been proposed as a new standard laboratory aquatic macrophyte test species for the registration of pesticides. The main objectives of this investigation were to determine the power of Myriophyllum sibiricum and Myriophyllum spicatum toxicity data derived from an outdoor microcosm bioassay, to evaluate the variation of 10 different aquatic plant endpoints and to calculate the minimum detectable difference for these endpoints, to determine the replication required to detect ecologically significant changes from control for these endpoints, and to make recommendations for future field studies with Myriophyllum spp. Control data from four different studies that characterized haloacetic acid toxicity with Myriophyllum spp. for durations of three to six weeks during the summer of 1999 with five treatment levels (n = 3), including control, were examined. Endpoint coefficient of variation ranged, on average, from 6 to 28%. Node number and plant length endpoints were consistently the most statistically powerful for both plant species. It was possible to detect approximately 30% change from control in both endpoints with high statistical power (beta = 0.2, alpha = 0.05, n = 3). The range of minimum detectable differences was 40 to 60% for the other endpoints. Replication to detect a > or = 25% change from control would require an n of 2 to 21, depending on the endpoint. Myriophyllum sibiricum had slightly lower coefficients of variation and thus required fewer replicates than M. spicatum to be statistically significantly different from control values. Variation within microcosm studies was not significantly different from that of controlled laboratory studies, implying that most of the variation observed in the field is inherent in the plants. Based on statistical sensitivity, ecological relevance, and toxicological sensitivity, we recommend using plant length and root endpoints as indicators of toxicity under field conditions.

Comparing growth development of Myriophyllum spp. in laboratory and field experiments for ecotoxicological testing

“…Tables 1 and 2). Growth results presented in this study were similar to published data (Forney and Davis 1981;Getsinger et al 1982;Turgut and Fomin 2001;Hanson et al 2001Hanson et al , 2003Stesevic et al 2007). In terms of the parameter growth rate, Myriophyllum spp.…”

“…is widely considered as a suitable bioassay plant for the detection of herbicidal activity (Forney and Davis 1981;Paterson and Wright 1987;Selim et al 1989;Green and Westerdahl 1990;Netherland and Getsinger 1992;Hanson et al 2002Hanson et al , 2003Turgut 2005) and has been proposed as a potential candidate for pesticide toxicity. A new bioassay with M. spicatum for evaluating phytotoxic effects in water or water-sediment systems was reported recently .…”

Application of in-situ bioassays with macrophytes in aquatic mesocosm studies

“…The CV of about 38% in Myriophyllum and 34-37% in Potamogeton in the control was comparable with the study of Coyner et al (2001) and Cedergreen et al (2004) who report CV's of about 33% (dry weight in Potamogeton pectinatus) and 50% (relative growth rate in M. spicatum), respectively. According to Hanson et al (2003), variation in macrophyte endpoints depends on the time of pesticide application and increases with study duration because of dependence on absolute growth rates over the exposure period. This would explain the higher variation in our results compared to the relatively short study with late application of Hanson et al (2003), who report CV's in plant length from 6.3% to 16.5% and CV's in dry mass from 12.3% to 31.8%.…”

“…According to Hanson et al (2003), variation in macrophyte endpoints depends on the time of pesticide application and increases with study duration because of dependence on absolute growth rates over the exposure period. This would explain the higher variation in our results compared to the relatively short study with late application of Hanson et al (2003), who report CV's in plant length from 6.3% to 16.5% and CV's in dry mass from 12.3% to 31.8%.…”

Variability in Nontarget Terrestrial Plant Studies Should Inform Endpoint Selection

“…However, it is important that the selected endpoint is statistically reliable (Green 2015(Green , 2016. Previous evaluations of variability and statistical detectability in toxicity tests have been conducted for aquatic plant species (Brain et al 2004(Brain et al , 2005Hanson et al 2003;Sanderson et al 2009;Knauer et al 2006) and for mesocosms (Kraufvelin 1998) but have not been explored to such a degree for terrestrial plants. Previous evaluations of variability and statistical detectability in toxicity tests have been conducted for aquatic plant species (Brain et al 2004(Brain et al , 2005Hanson et al 2003;Sanderson et al 2009;Knauer et al 2006) and for mesocosms (Kraufvelin 1998) but have not been explored to such a degree for terrestrial plants.…”