# Selecting Bioassay Test Species at the Screening Level of Soil Ecological Risk Assessments
## 3 Results and Discussion
### Correlation of EtoxRI and Ecotoxicological Data  
Our comparison of EtoxRI with ecotoxicological data showed that the test species that best reflected the overall ecotoxicity of field soils were in the order of soil algae (_C. infusionum_), soil nematodes (_C. elegans_), and plants (especially acute assays for _O. sativa_ and _V. radiata_); their correlation coefficients were 0.979 (\(p<0.01\)), 0.928, 0.925, and 0.886 (\(p<0.05\)), respectively. Other species had lower correlation coefficients. Therefore, in this study, we determined that soil algae, soil nematodes, and plants are ideal for well-represented assays that reflect site-specific SERA. According to [PERSON] et al. [1] (the progenitors of the triad approach), commercial test kits for luminescent bacteria (ostracod and cladoceran) are recommended as toxicology tools for tier 1. For tier 2, the acute toxicity test using earthworms and avoidance tests for soil invertebrates are suggested. Finally, for tier 3 toxicology tools to evaluate the potential risk of soils for entire ecosystems, plant assays, reproduction tests using earthworms and collembola, and enchytraeid tests are recommended for soil bioassays, whereas algae tests, aquatic plant tests, and bioassays using _Daplnia magna_ are suggested for soil extract bioassays. The findings of this study raise uncertainties that the list of test species may not adequately reflect the ecotoxicity of field soils for site-specific SERA. Therefore, it is assumed that discussion on the recommended bioassays for site-specific SERA will be necessary. Figure 2: Soil bioassays using soil organisms, where (**a**) and (**b**) show the growth rates in plant assays on mung bean (_V. radiata_), and rice (_O. sativa_) after a 7-day (left) and 14-day exposure (right), respectively, (**c**) shows the survival rate of earthworms (_E. André_) after a 14-day exposure, (**d**) represents the adverse effects on cellomba (_F. candidia_) after 14 days (left; the survival of adults) and 28 days (right; the reproduction of juvenile), and (**e**) and (**f**) show the reproduction rate of the soil nematode (_C. elegans_) after a 24 h exposure and the chlorophyll intensity of soil algae (_C. infusionum_) after a 6-day exposure, respectively. Line bars indicate standard deviation, and the asterisk (*) indicates a significant adverse effect compared with the control (R). The hash (#) indicates a significant positive effect compared with the R.  
We compiled a list of the test species used in triad approach studies (Table 3). The ecotoxicological LoE in the tier 1 assessment was mainly estimated from bioassays using only one soil type. Only two or three studies performed bioassays using two or three soil species. Two other studies used no soil species at all [22; 23]. Most studies performed bioassays using plants or earthworms. Bioassays using aquatic organisms were evaluated using soil eluates, extract, and leachate, among others, for the tier 1 triad approach. Among them, _D. magna_ and _Aliivibrio fischeri_ were usually used as test species [23; 24; 25; 26; 27; 28] as they are reliable, rapid, and cheap [1; 29]. Five studies among nine researched used algae or plant assays in solution tests [27; 28; 30; 31; 32]. Few studies selected test species based on the ecological relevance of the site (Table 3). The main justifications for the selection of a test species are common use in soil ecotoxicity tests, simplicity, and low cost of the assay. The author [PERSON] [33] suggested the following criteria to select test species for ERA: practicability, including feasibility and cost-effectiveness; acceptability, including standardization, reproducibility, and validity; and ecological meaning, such as sensitivity and ecological realism. In addition, as identified in this study, performing bioassays by selecting test species based on economic reasons does not achieve the goal of screening for ecological risk. Using a single species is also likely to underestimate or overestimate the ecotoxicological risk when screening for a SERA.