Toxicity testing with the collembolans Folsomia fimetaria and Folsomia candida and the results of a ringtest
3 Testing results obtained at NERI, 1994 to 1999
3.1 Introduction
Since 1992, plenty of toxicity tests and experiments have been conducted with F. fimetaria at Department of Terrestrial Ecology, Danish National Environmental Research Institute (NERI). This section describes a compilation of a subset of these tests to illustrate the intra-laboratory variability of an experienced testing facility. The data has previously been reported to Environment Canada (Krogh, 2004).
The database included the control reproduction observed in 57 tests with F. fimetaria (Annex 4). The procedure followed was a standard test guideline in effect at the laboratory since 1994 (Krogh, 1995; Wiles and Krogh, 1998). The tests were performed during a period of 6 years, potentially representing variability of culture health and performance properties. Different soil types ranging from sandy soils to clay soils were used in the tests.
3.2 Performance
The mean survival of initially 20 adult F. fimetaria, 10 females and 10 males, and their reproduction in the 3 week standard tests were: 17.7 [17.2-18.2] and 430.8 [405-457], respectively; for frequency distributions see Fig. 3; the reproduction was normally distributed, P>15% (Kolmogorov’s D statistic). 5% of the tests would have a reproduction £233 according to the normally distributed reproduction. The average CV was 18.1 [15.4-21.2][5] None of the tests had a mean reproduction less than 100, but 7% had a coefficient of variation CV>30% (Annex 4), which is the validity criteria of the ISO F. candida test (ISO, 1999). Two of the CV’s qualified as outliers, according to the validity criterion and 14% of the tests had an average adult mortality >20%, the validity criteria, and 2% a mortality >30%.
F. fimetaria performed generally well in all soils tested, so when reduced performance was observed this might be the result of other factors, such as health condition, seasonality or feeding condition.
3.3 Influence of soil type
Linking soil properties to collembolan performance, i.e. survival and reproduction, must be done with caution, due to the fact that the NERI data does not originate from experimentally designed studies with soil factors applied as treatments, but from independently assessments of the performance. Thus, the level of performance in the tests may have been caused by the actual condition of the test animals. Uncontrolled microbial factors differing from test to test may exert an influence on performance too.
Fig. 3. Frequency distributions of surviving F. fimetaria adults of the initial 20 males and females and their reproduction for each replicate sample analysed, n=243, the normal distribution with mean 433.7 and variance 14,924 is included on the reproduction graph.
To explore the relationships between the two performance measurements and soil characteristics, the correlations are given in Table 1. Adult survival was not correlated with soil constituents but reproductive output, in terms of number of juveniles, was significantly positively correlated with clay and silt but was negatively correlated with sand content of the soil.
3.4 Conclusion
The soil particle fractions clay and silt was positively correlated with the reproduction, while sand was negatively correlated with the reproduction. The performance of F. fimetaria was generally good for all soil types tested, with only less than an average of 200 juveniles per replicate in a control series observed in 2 tests. Survival was on the average 88.5% and was not affected by the soil types. Test performance was equivalent to the requirements for the F. candida test and therefore supports the same validity criteria as stated in ISO 11267: a mean maximum adult mortality of 20%, a mean minimum reproductive output of 100 juveniles in the controls with a maximum coefficient of variation (CV) of 30%.
The tests with F. fimetaria met the validity criteria as defined in the ISO 11267 standard (ISO, 1999) of at least 100 juveniles in the controls and in 91% of the tests the CV<30%
Table 1 Pearson correlation coefficients and the significance of the correlations between the soil characteristics and performance data of F. fimetaria from standard tests. Number of observations, n=243.
| Correlation, r |
Correlation strength, r² |
Significance | ||
| Clay | Organic matter | 7.5% | 0.6% | 24% |
| Silt | Organic matter | 14% | 1.9% | 3% |
| Silt | Clay | 91% | 83% | <0.01% |
| Sand | Organic matter | -22% | 5.0% | 0% |
| Sand | Clay | -95% | 90% | <0.01% |
| Sand | Silt | -99% | 97% | <0.01% |
| Adult | Organic matter | 1.5% | 0.0% | 92% |
| Adult | Clay | 4.2% | 0.2% | 66% |
| Adult | Silt | 4.0% | 0.2% | 65% |
| Adult | Sand | -3.5% | 0.1% | 71% |
| Juveniles | Organic matter | -1.0% | 0.0% | 87% |
| Juveniles | Clay | 17% | 2.9% | 0.75% |
| Juveniles | Silt | 22% | 4.6% | 0.07% |
| Juveniles | Sand | -21% | 4.3% | 0.1% |
| Juveniles | Adult | 34% | 11% | <0.01% |
[5] Confidence intervals of the log-normal distribution: 
(Olsson, 2005) obtained by back-transformation.
Version 1.0 December 2008, © Danish Environmental Protection Agency