Codificación

If additional species (not belonging to the standard test species mentioned in Chapter 5) are tested, it is necessary to consider which toxicity value should be used in the risk assessment, at least if the number of available toxicity data was not high enough to apply the Species Sensitivity Distribution approach. According to the present guidance, 'if a considerable number of additional species was tested in valid studies, then it is possible that the uncertainty factors that are applied to the lowest toxicity value could be lowered by up to an order of magnitude' (SANCO, 2002). It is not further specified how many additional data would be needed to allow for lowering the assessment factor, and to our experience, this option is not often applied in practice. Although more species are tested and thus information on the differences in sensitivity between species is available, the risk assessment is most often still based on the most sensitive species using the default assessment factors. The number of species to be tested according to pesticide legislation effectively sets the first-tier level of protection in the effects assessment. Consequently, when more data are available and the risk assessment is still based on the lowest value without adjusting the trigger value, the average level of protection may exceed the level implied by the provisions of the PPP Regulation.

Approaches considered by EFSA 6.3.1

In 2005, the EFSA PPR Panel published an opinion on the approaches to deal with additional toxicity data, taking into account that the same average level of protection should be maintained.

Option 1

As a first option, the PPR Panel proposed an alternative approach of taking the geometric mean of comparable endpoints within a taxonomic group when more than one species is tested, where the legislation only required one species (EFSA, 2005b). It was shown that this would ensure at least the same average level of protection as implied by the Directive, and avoid most of the increase in conservatism when additional species are tested. This was based on the assumption that toxicity data were normally distributed on a logarithmic scale. Later research (EFSA, 2008) showed that this is true for a wide range of distributions that are symmetric and unimodal (single peak) on a logarithmic scale, and also for asymmetric unimodal distributions where the long tail is to the left. It is also true for asymmetric distributions with long tails to the right2 _{and for some examples}

of bimodal distributions, provided that the standard uncertainty factor includes sufficient allowance for between-species variation in toxicity, which seems likely.

The latter work is mainly based on distributions of acute toxicity data. It remains to be investigated whether the same procedure can be used for chronic toxicity data as well. NOECs may be over/underestimates (e.g. due to wide dose spacing and limited power to detect effects often caused by small sample size). The PPR Panel recommended, however, using the geometric mean for both acute and reproductive toxicity, when multiple species are tested within a taxonomic group. The first tier AF of 10 or 100 should be applied to this geometric mean value of available toxicity data to derive a RAC.

It should be noted that 'taxonomic group' can be interpreted in different ways. For instance, crustaceans and insects represent different taxonomic groups on the phylum level but are sometimes grouped into the

2 _{Distributions of acute toxicity data often have long tails to the right on the natural scale, but this is reduced or removed on}

taxonomic group of arthropods. The default approach should be to treat them as different groups unless scientific arguments can be raised to consider them as one group.

Option 2

For those organism groups where the legislation requires that at least two species are tested, this implies a higher level of protection in the effects assessment in the first tier. In this case, a different procedure is required when additional species are tested. The minimum is then replaced by the ith _{lowest toxicity value}

depending on the sample size available, and divided by the current assessment factor (Method 2 described in EFSA, 2005b).

Procedure when more than two species are tested within a taxonomic group: 1. Order the data so that the values are increasing.

2. Choose from the ordered data the ith_{value where i is determined from Table 6-1 according to the}

sample size.

3. Divide the obtained data value by the current assessment factor.

This table seems to be less relevant if toxicity data for more than five fish species or more than eight taxa of the sensitive non-vertebrate taxonomic group are available, because in that case the SSD approach seems to be a more scientific solution.

Table 6- 1

Sample-size dependence of order statistics to be used with current assessment factors to achieve at least the same level of protection as the current procedure for a sample of size 2. Sample size Position in ordered list of data (i)

3-4 1

5-7 2

8-10 3

11-13 4

For deciding whether species belong to the same taxonomic group, again the default approach should be to treat them as different groups unless scientific arguments can be raised to consider them as one group.

Proposal for the derivation of RACs when a limited number of additional single 6.3.2

species toxicity tests is available

In some cases additional ecotoxicity data may be available, but their number is too low to apply the SSD approach. For this situation, it is proposed to use the geometric mean of the available toxicity values within a taxonomic group (Option 1 above; Table 6-2).

Table 6- 2

Proposal for the derivation of RACs for aquatic organisms when a limited number of additional single species toxicity tests is available. When applying this approach scientific arguments should be given why the selected toxicity data (on which the geomean is based) concern the same taxonomic group relevant for the risk assessment.

Taxonomic group Number of toxicity data for different taxa of the relevant taxonomic group

RAC Field exposure concentration Fish and/or other aquatic vertebrates < five acute LC50's Geomean LC50/100 PECmax

Fish and/or other aquatic vertebrates < five chronic NOECs (or chronic EC10's) Geomean NOEC/10 PECmax or PECTWA

Invertebrates and/or primary producers < eight acute EC50's Geomean EC50/100 PECmax

Invertebrates and/or primary producers < eight chronic NOECs (or chronic EC10's) Geomean NOEC/10 PECmax or PECTWA

The benefit of this approach is that all species groups are treated in the same way and that methods do not have to change in the future when more than one standard test species is required for a particular group of species, which implies that in the new situation the level of protection achieved will be different compared to the old situation. The first tier AF of 10 or 100 should be applied to this geometric mean value of available toxicity data to derive a RAC.