Simazine – summary of aquatic toxicity data

Background

The following summary has been produced from information presented in the original draft assessment report on simazine (December 1996), the relevant ECCO reporting table and endpoint sheet. It has also incorporated relevant data submitted to the RMS and considered by the WG(E) after the ECCO meeting (see Addendum 4 Sept 2001, which was discussed at the October 2001 WG(E) meeting).

Acute risk

Following evaluation of all the available acute laboratory data on simazine, the following key endpoints were identified:

96h LC50 of 42.33 mg as/l for the zebrafish (Brachydanio rerio),

48 h EC50s for Daphnia magna of >100 mg as/l.

Studies showed simazine to be of high toxicity to freshwater algae. Scenedesmus subspicatus was the most sensitive species tested, with an EbC50 value of 0.042 mg as/l from a study using the technical active substance. A study on the aquatic higher plant Lemna gibba gave a 14-day EC50 (based on frond growth) of 0.32 mg as/l.

On the basis of the above data an acute risk was identified regarding the risk to algae and Lemna, i.e. TERs assuming 5% drift at 1 m were less than the appropriate Annex VI trigger value. Due to this concern the RMS and ECCO considered a range of microcosm and mesocosm studies, however these were of limited use and hence could not be used. Therefore, the RMS and ECCO considered the role of risk mitigation and identified ‘safe uses’ providing that suitable measures were taken. ECCO identified that the TER at 5 m for both algae and aquatic higher plants would be greater than the Annex VI trigger value of 10.

Subsequent to the original assessment further data were submitted which indicated that the ‘ecologically acceptable concentration’ (EAC) was 0.05 mg/l. When this endpoint was compared to the initial PEC at 1 m, at TER of 2 was determined. This TER (equivalent to an uncertainty factor of 2) was considered insufficient to address the uncertainties in the risk assessment, therefore, the TER at 5 m was determined. The TER at 5 m was 17 and this considered to address the uncertainties and hence provide sufficient protection. Therefore on the basis of this, the ‘safe concentration’ could be determined to be 0.003 mg/l. It should, however be noted that this concentration is due to the fact that PECs and hence ‘safe concentrations’ are determined at set distances, i.e. 1, 5, 10 m etc rather than determined from toxicity data alone. Therefore, the actual safe concentration lies somewhere between 0.025 mg a.s./l and 0.003 mg a.s./l (see Addendum 4, Sept 2001).

Marine species:

Some acute toxicity data were submitted for marine species, however these did not suggest that marine species are any more sensitive to simazine than freshwater species.

Chronic risk

As regards the long-term or chronic risk to aquatic life, the RMS and ECCO meeting accepted that the lowest NOEC for fish was 3.4 mg a.s./l which was from a study which used the rainbow trout. The NOEC for aquatic invertebrates was 0.036 mg a.s./l which came from a Daphnia magna study

Risk to sediment dwelling invertebrates

As regards the risk to sediment dwelling invertebrates, it was concluded that further data. Further data have been submitted and these indicated that the NOEC was 0.2 mg a.s./l (see Data requirement 3.4 in the Simazine evaluation table 5043/VI/98 rev 10, 12-10-01).

Bioaccumulation

A bioaccumulation study was submitted which indicated a low potential for simazine to bioaccumulate, i.e. BCFs <1.

Conclusion

On the basis of the assessment of the available data the ‘safe concentration’ is considered to lie between 0.025 and 0.003 mg a.s./l.

Appendix 1

Draft endpoint sheet for simazine

Toxicity data for aquatic species (most sensitive species of each group) (Annex IIA, point 8.2,
Annex IIIA, point 10.2)
Group / Test substance / Time-scale / Endpoint / Toxicity
(mg a.s./l)
Laboratory tests
fish / active substance / 96 hours / LC50 / 42.33*
‘Gesatop 90 WG’ / 96 hours / LC50 / >17.19
‘Gesatop 500 SC’ / 96 hours / LC50 / >27.65
active substance / 28 day / NOEC / 3.4
Invertebrates / active substance / 48 hours / EC50 / >100*
‘Gesatop 90 WG’ / 48 hours / EC50 / 14.8
‘Gesatop 500 SC’ / 48 hours / EC50 / 26
active substance / 21 day / NOEC / 0.036
algae / active substance / 72 hours / EC50 / 0.042*
‘Gesatop 90 WG’ / 72 hours / EC50 / 0.0531
‘Gesatop 500 SC’ / 72 hours / EC50 / 0.07
aquatic plants / active substance / 14 days / EC50 / 0.32*
Microcosm or mesocosm tests
Three published studies were submitted. These were not designed or conducted for regulatory purposes, generally lacked detail, and were of uncertain relevance to the proposed uses. Hence, these data were of very limited use in the risk assessment.

* These values were used in the risk assessment

Toxicity/exposure ratios for the most sensitive aquatic organisms (Annex IIIA, point 10.2)

Application
rate
(kg as/ha) / Crop / Organism / Time-scale / Distance
(m) / TER / Annex VI
Trigger
2.0 / maize / fish / acute / 1 m / 1283 / 100
invertebrates / acute / 1 m / 3030 / 100
algae / short term / 1 m / 1.27 / 10
algae / short term / 5 m / 10.5 / 10
aquatic plants / short term / 1 m / 9.7* / 10
aquatic plants / short term / 5 m / 80 / 10
fish / long term / 1 m / 103 / 10
invertebrates / long term / 1 m / 1.1 / 10
long term / 5 m / 10** / 10

* TER is 12.8 for the 1.5 kg a.s/ha application rate. ** Using time-weighted average PEC

Risk from aerial application (assuming overspray) considered to be unacceptable.

In addition, consideration of drainage contamination needed at Member State level.

Bioconcentration
Bioconcentration factor (BCF) / 1
Annex VI Trigger for the bioconcentration factor / 100