2,6-di-tert-butylphenol

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.001 mg/L

Assessment factor:

50

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.004 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0 mg/L

Assessment factor:

500

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

10 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.317 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.032 mg/kg sediment dw

Extrapolation method:

equilibrium partitioning method

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

0.697 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

60 mg/kg food

Assessment factor:

90

Additional information

Effects on Aquatic Organisms

Micro-organisms

A 3 hour respiration inhibition study carried out according to OECD 209 was used to assess the effect of 2,6-DTBP on STP micro-organisms. An EC₅₀of >1000 mg/l was determined (no NOEC was determined). According to the TGD an AF of 100 should be applied to derive a PNEC_STP of 10 mg/l.

Species	Endpoint	Comments	Reference
Activated sludge respiration inhibition testing	EC50(3h contact time) = >1000 mg/L	-	Sewell I.G. (1991) Activated sludge respiration inhibition test, Safepharm Laboratories Ltd., Derby, UK, SI Group, Report No S0052/E361

 

Water compartment

The current strategy for deriving a protective PNEC_wateroutlined in the Technical Guidance Document for risk assessment (2003), indicates that the appropriate assessment factor should be applied to the lowest acute L(E)C₅₀value obtained from toxicity testing in fish, aquatic invertebrate and algal species. In the event that chronic toxicity data are available from three separate trophic levels, the lowest NOEC value is used with an assessment factor of 10 applied for fresh water and 100 applied for marine water.

Two long-term tests (NOEC or EC₁₀) with species representing different living and feeding conditions are available: Toxicity to aquatic algae and cyanobacteria and Long-term toxicity to aquatic invertebrates with the latter being conducted in the most sensitive species according to the acute tests. According to Guidance on information requirements and chemical safety assessment Chapter R.10: Characterisation of dose [concentration]-response for environment, section R.10.3.1 and R.10.3.2 under this circumstance an assessment factor of 50 is applicable to the NOEC of the long term study in daphnia magna to derive the PNEC aqua (freshwater) and an assessment factor of 500 is applicable to the NOEC of the long term study in daphnia magna to derive PNEC_aqua(marine water)

Detailed below is an assessment of the available data ecotoxicological data together with recommendations for the endpoints which should be used to determine the Predicted No Effect Concentration for 2,6-DTBP in the fresh water environment (PNEC_{fresh water}) and marine environment (PNEC_{marine water}): -

Fish

Four studies were conducted in fish. Two acute studies (rainbow trout and zebra fish) and two prolonged toxicity tests (14 days; rainbow trout and fathead minnows). From the 14 day studies conducted in fathead minnows and rainbow trout it was also possible to determine 96 h LC₅₀values thereby satisfying the requirements of an acute toxicity test. Due to a poor dose response relationship the results from the 14 day prolonged toxicity test with rainbow trout were considered to have lower reliability than the fathead minnow results.

The two rainbow trout 96h LC₅₀results were greater than the highest value tested. The 96 h LC₅₀fathead minnow result therefore represents the lowest and most accurate result for basing the PNEC. 

There were no long-term fish studies.

Species	Endpoint	Comments	Reference
Fish toxicity	96 h LC50in rainbow trout = >1.0 mg a.i./L	Highest value tested-no effects found	Sewell I.G. (1991) Acute toxicity to rainbow trout, Safepharm laboratories Ltd., Derby, UK, SI Group, Report No. 47/1612
	96 h LC50in zebra fish = 13 mg/L, LC0(96 h) = 10 mg/L	nominal concentrations	Rufli H. (1987) Report on the test for acute toxicity of TK 12891 to Zebra fish, OECD-Guideline No. 203 Paris (1984), US EPA OTS 86-870000305, Ciba-Geigy Ltd., Report No. 87 40 50
	96 h LC50in rainbow trout = >0.10 mg a.i./L	Highest value tested	Surprenant D.C. (1989) Acute Toxicity of 2,6-di-tert-butylphenol to Rainbow Trout (Salmo gairdneri) during a 14-day flow-through exposure, Springborn Life Sciences, Albemarle, Report No. 89-05-2948
	14 day LC50Rainbow Trout = 0.74 mg/L		Surprenant D.C. (1989) Acute Toxicity of 2,6-di-tert-butylphenol to Rainbow Trout (Salmo gairdneri) during a 14-day flow-through exposure, Springborn Life Sciences, Albemarle, Report No. 89-05-2948
	96 h LC50for fish (fathead minnow)= 1.4 mg a.i./l NOAEL (14 days) = 0.30 mg/L.	KEY STUDY	Surprenant D.C. (1989) Acute toxicity of 2,6-di-tert-butylphenol to fathead minnows (Pimephales promelas) during a 14-day flow-through exposure, Springborn Life Sciences, Inc., Albemarle, Report No. 86-12-2876
	7 day LC50fathead minnows = 1.1 mg/L		Surprenant D.C. (1989) Acute toxicity of 2,6-di-tert-butylphenol to fathead minnows (Pimephales promelas) during a 14-day flow-through exposure, Springborn Life Sciences, Inc., Albemarle, Report No. 86-12-2876
	14 day LC50fathead minnows = 1 mg/L		Surprenant D.C. (1989) Acute toxicity of 2,6-di-tert-butylphenol to fathead minnows (Pimephales promelas) during a 14-day flow-through exposure, Springborn Life Sciences, Inc., Albemarle, Report No. 86-12-2876

 

Invertebrates

Species	Endpoint	Comments	Reference
Invertebrate toxicity	48 h EC50in Daphnids = 0.45 mg a.i./L	NOEC (48 h) = 0.076 mg a.i./L	Surprenant D.C. (1989) Acute Toxicity of 2,6-Di-tert-Butylphenol to Daphnids (Daphnia magna), Springborn Life Sciences, Albemarle Corporation, Report No. 88-12-2893
	96 h EC50in Gammarids = 0.60 mg a.i./L		Surprenant D.C. (1988) Acute toxicity of 2,6 di-tert-butylphenol to Gammarids (Gammarus fasciatus) during a 4 day flow-through exposure, Springborn Life Sciences, Inc., Albemarle, Report No. 88-12-2881
	21 d NOEC in Daphnia magna = 0.035 mg/L test material (measured geometric mean) based on parental mortality & growth parental body length	KEY STUDY LOWEST ENDPOINT	Migchielsen.M.J.H. (2014) Daphnia Magna, Reproduction Test with 2,6-Di-Tert-Butylphenol (Flow-Through), WIL Research Europe B.V. Hambakenwetering 7 5231 DD ‘s-Hertogenbosch The Netherlands, Report No. 503524

The long term Daphnid study provides the lowest endpoint. 

 

Aquatic Plants

Species	Endpoint	Comments	Reference
Algal toxicity	72 h IC50for algae = 1.2 mg a.i./l (TWA), NOEC = 0.64 mg a.i. /L (TWA)	KEY STUDY	Hoberg J.R. (1991) 2,6-di-tert-butylphenol (DTBP) toxicity to the freshwater green alga (Selenastrum capricornutum), Springborn Laboratories, Inc., Albemarle, Report No. 91-7-3822
	96 h EC50in Green Algae= 0.56 mg/l (TWA)	Poor recovery of test substance	Giddings J.M. (1989) Toxicity of 2,6-Di-Tert-Butylphenol to the Freshwater Green Alga Selenastrum capricornutum, Springborn Live Sciences, Inc., Albemarle Corporation, Report No. 88-11-2846

 

Two studies were conducted using the guideline standard test organism, Selenastrum capricornutum, over the guideline standard time period of 96 h. The study conducted by Giddings J.M. (1989) had poor recovery of test substance and the reliability of the study was therefore reduced. For this reason the study conducted by Hoberg J.R. (1991) was considered to be the key study. This study provides both short-term and long-term results.

Summary Water Compartment

From the aquatic tests described above, the proposed PNEC_{fresh water}0.0007 mg a.i./L,is based on the most sensitive species which was found to be invertebrates with an assessment factor of 50 (two long-term studies available, with daphnids being the most sensitive species). The proposed PNEC_{marine water}0.00007 mg a.i./L, is based on the application of an additional assessment factor of 10 to the assessment factor of 50 applied to the NOEC value obtained in the invertebrate toxicity study.

 

Sediment

Weight of evidence approach

PNEC calculation based on terrestrial Read-Across data

Versonnen et al. 2014 (Sci Total Environ.2014 Mar 15;475:123-31. doi: 10.1016/j.scitotenv.2013.10.058. Epub 2013 Nov 14. Analysis of the ecotoxicity data submitted within the framework of the REACH Regulation: part 4. Experimental terrestrial toxicity assays. Versonnen B, Tarazona JV, Cesnaitis R, Sobanska MA, Sobanski T, Bonnomet V, De Coen W.) describe that also for terrestrial endpoints “Standard REACH information requirements can be adapted on the basis of REACH column 2 rules for adaptation mentioned above, as well as on the basis of the 'general rules for adaptation' listed in Annex XI of the REACH Regulation. These general rules are applicable to all endpoints and include weight of evidence (WoE) approaches, qualitative or quantitative structure-activity relationship ((Q)SAR), in vitro methods, grouping of substances and read-across, indications that testing is technically not possible, and tailored exposure-driven approaches”.
Therefore read across data from structural analogues in the “phenols” category, using the OECD QSAR Toolbox 3.2.0.103 was generated:

Read across data

Test/OECD TG	Predicted NOEC for 2,6-DTBP, mg/kg soildw	Range of NOEC values used for read across, mg/kg soildw
Long-term toxicity to terrestrial invertebrate (earthworm)/OECD 222	800	125 – 1250
Long-term toxicity to terrestrial plants: seedling emergence and growth/OECD 208	251	113-370
Long-term effects on soil microorganisms: nitrogen transformation test/OECD 216	399	2 – 1250

(see below under “Data basis- Newly generated data” for more details)

The read across assessments were conducted according to the relevant guidance documents and 2,6-DTBP falls in all three cases into the applicability domain (please see chapter “Data basis” and Annex 2 for detailed prediction reports in TPRF (Toolbox Prediction Reporting Format)). Therefore the consortium regards this data to be scientifically valid.
Following ECHA guidance on PNECsoil calculation using assessment factors (Table R.10-10 in Chapter R.10) the PNEC soil can be calculated using an assessment factor (AF) of 10 (with three long-term NOEC values for three trophic levels available) on the lowest of the three NOECs (251 mg/kg soil dw).
Accordingly the PNEC_{dry soil}would be 25.1 mg/kg soil dw.
Using as a worst case the lowest experimental NOEC value for the analogues (2 mg/kg soildw) with an AF of 10 the respective PNEC_{dry soil}calculates out as 0.2 mg/kg soil dw.
All NOECs over all trophic levels fall into a relatively narrow range and the NOECs predicted for 2,6-DTBP are well inside this range. Therefore the consortiums deems these results to be scientifically justified and applicable for hazard and risk assessment.

 

PNEC calculation based on newly generated aquatic toxicity data using the EPM method

Calculation of PNEC for sediments using the equilibrium partitioning method (EPM)

To calculate PNEC for freshwater sediment, marine sediment and soil the guidance on how to do this is on Chapter R.10 and R.16.

The equations R.10-2, R.10-3, R.10-5 in ECHA guidance Chapter R.10

The equations use default values and data you have already on the substance.

PNEC_comp= K_comp-water/RHO_comp* PNEC_water* 1000

where,

comp' = environmental compartment, e. g. freshwater sediment, marine sediment, suspended matter or soil;

PNEC_comp= Predicted No Effect Concentration in wet comp, mg/kg of wet comp;

K_comp-water= comp-water partitioning coefficient, m³/m³;

RHO_comp= bulk density of wet comp, kg/m³ (= 1150 given); and

PNEC_water= Predicted No Effect Concentration in water (freshwater or marine), mg/L.

The unknown term in the above equation is the partitioning coefficient, K_comp-water, which is derived from equation R.16-7 in ECHA guidance Chapter R.16:

K_comp-water= F_aircomp* K_air-water+ F_watercomp+ F_solidcomp* (Kp_comp/1000) * RHO_solid

where,

F_aircomp= fraction of air in comp, m³/m³ -- only relevant for soil; F_airsoil= 0.2 m³-air/m³-soil, from Table R.16-9

K_air-water= air-water partitioning coefficient;

F_watercomp= fraction of water in comp, m³/m³; F_watersusp= 0.9 m³-water/m³-suspended matter, F_watersed= 0.8 m³-water/m³-sediment, F_watersoil= 0.2 m³-water/m³-soil, from Table R.16-9

F_solidcomp= fraction of solids in comp, m³/m³; F_solidsusp= 0.1 m³-soilds/m³-suspended matter, F_solidsed= 0.2 m³-soilds/m³-sediment, F_solidsoil = 0.6 m³-soilds/m³-soil, from Table R.16-9

Kp_comp= solids-water partitioning coefficient in comp, L/kg;

Kp_comp= Foc_comp* Koc                  equation R.16-6

where,

Foc_comp= weight fraction organic carbon in comp solids, kg-oc/kg-solids;

Foc_susp= 0.1 kg-oc/kg-solid

Foc_sed= 0.05 kg-oc/kg-solid

Foc_soil= 0.02 kg-oc/kg-solid

Koc = partitioning coefficient organic carbon-water (4493 L/kg -- from data set for the substance being registered)

RHO_solid= density of the solid phase, kg/m³ (= 2500 given).

Compartment	PNECcomp	Kcomp-water	RHOcomp	PNECwater	Faircomp	Kair-water	Fwatercomp	Fsolidcomp	Kpcomp	RHOsolid	Foccomp	Koc	HLC	v. p	MW	water solubility
	mg/kg of wet comp	m3/m3	kg/m3	mg/L	m3/m3		m3/m3	m3/m3	L/kg	kg/m3	kg/kg		Pa-m3/mole	Pa	g/mole	mg/L
freshwater sediment	0.0689	113	1150	0.0007	NA	NA	0.9	0.1	477	2500	0.1	4493
marine sediment	0.00689	113	1150	0.000070	NA	NA	0.9	0.1	477	2500	0.1	4493
soil	0.0556	135	1150	0.0007	0.2	0.0145	0.2	0.6	95.4	2500	0.02	4493	34.3	1.01	206.33	4.11

 

PNEC_freshwater= 0.0007 mg/L

PNEC_{marine water}= 0.000070 mg/L

Koc = 4493

MW = 206.33

water solubility = 4.11 mg/L

vapour pressure = 1.01 Pa

PNEC_{freshwater wet sediment}= 0.0689 mg/kg ww

PNEC_{freshwater dry sediment}= 0.317 mg/kg dw

PNEC_{marine wet sediment}= 0.00689 mg/kg ww

PNEC_{marine dry sediment}= 0.0317 mg/kg dw

PNEC_{wet soil}= 0.0556 mg/kg ww

PNEC_{dry soil}= 0.063 mg/kg dw

Conclusion on sediment toxicity

Comparison of PNEC_{dry soil}:

Data base	PNECdry soil
Based on three available long-term terrestrial studies for the registered substance (this dossier)	0.693 mg/kg soil dw (experimentally determined)
Based on the EPM method (calculation performed as described above)	0.063 mg/kg dwn (calculated with EPM-method)

 

The comparison of PNEC_{dry soil}values shows that using the Daphnia magna reproduction test data in combination with the EPM method leads to the lowest (=more conservative) PNEC_{dry soil}value. The comparison with the respective value derived from terrestrial long-term studies clearly indicates that the EPM value is significantly more conservative. Based on the outcome of this analysis, the registered substance has no properties which makes it more toxic to soil organisms than predicted by the EPM method. It can be assumed that this is also true for sediment organisms. As shown for the soil compartment, we consider the calculation of the PNEC sediment by the EPM method as conservative. Hence, following PNECs will be used for the risk assessment.

Since the log Pow is < 5, an additional factor of 10 is not needed.

PNEC_{freshwater dry sediment}= 0.317 mg/kg dw

PNEC_{marine dry sediment}= 0.0317 mg/kg dw

Secondary Poisoning of Birds and Mammals

PNECoral

The PNEC_oral(60 mg/kg food) was based on the NOAEL of 270 mg/kg bw/d from the rat oral 90 day study with a conversion factor of 20 to convert from mg/kg bw/day to mg/kg food/day and an assessment factor of 90 for the extrapolation from mammals to birds according to Guidance on information requirements and chemical safety assessment Chapter R.10: Characterisation of dose [concentration]-response for environment, section R.10.8.2, using equation R.10-8 and table R.10-13.

PNEC_oral= TOX_oral/ AF_oral                                              Equation R.10-8