Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

Short-term toxicity to fish

Three acute tests with two freshwater species are available (Onchorhynchus mykiss, Pimephales promelas) with 96 h LC50 values of 0.044, 0.097 and 0.638 mg/L. Concerning the effects on fish the study of Hodson et al. (1984) and the LC50=0.638 mg/L is preferred because the test performance fulfills mostly the requirements of the OECD Guideline 203, contrary to the other two tests.

Long-term toxicity to fish

One reliable key study is available on a fish early-life stage toxicity test performed on fathead minnow according to the OECD testing guideline 210 and GLP. The test was performed using a flow-through system with target test concentrations of 4.6, 10, 22, 46 and 100 µg/L. No effects on the mortality and reproduction were observed up to and including the highest tested concentration.  At the highest target concentration of 100 µg/l, analyses showed that recoveries of hydroquinone decreased as exposure progressed with recoveries ranging from 35% to 96%. However, the degradation product p-benzoquinone can also induce effects. Hence the contribution of this degradation product to the test item concentration should be considered.

The contribution of the degradation product p-benzoquinone in solution varied from 6.4 to 42 % (i.e. relative to the measured Hydroquinone concentration). Globally it has been observed that the contribution of p-benzoquinone decreases as test item concentration increases. At the highest target concentration of 100 µg/l of hydroquinone, its contribution was between 8 and 19% (i.e. relative to the measured Hydroquinone concentration). Considering the measured concentrations of both hydroquinone and p-benzoquinone, the recoveries ranged from 45 to 107%, consequently still outside the accepted range of 80-120%. However, it should be highlighted that the analytical method development and validation demonstrated that there is a rapid interconversion between hydroquinone and p-benzoquinone in samples, and therefore the real concentration of both substances is uncertain.

Hence, the NOEC of Hydroquinone can be expressed both in arithmetic mean concentration as recommended by the OECD Testing Guideline No 210, and in nominal concentration to take into account the effects of the degradation product and the uncertainties of the analytical measurement

The 32d NOEC has been determined to be 100 µg/L expressed in target concentration and 66 µg/L expressed in mean concentration measured.

Short-term toxicity to aquatic invertebrates

Four studies dealing with the acute toxicity of hydroquinone to Daphnia are available. The acute toxicity of hydroquinone to Daphnia magna was investigated in a study conducted equivalent or similar to OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test) under GLP and semi-static conditions. The daphnids (20 animals/concentration) were exposed to measured concentration of 0 (control), 0.029, 0.043, 0.074, 0.11, and 0.18 mg/L for 48 h. The test substance concentrations were measured by HPLC/UV. The endpoint examined was immobilization. The 48 h NOEC, EC50, and EC100 were determined to be 0.029, 0.061, and 0.11 mg/L based on mean measured concentrations. Provided that the formed degradation products are also of high ecotoxicity the evaluation of the test based on the concentration of the parent compound alone may overestimate its toxicity. Provided further that the total amount of toxic equivalents is stable during the exposure period the initial concentration is regarded as relevant concentration. Therefore, the daphnia test is re-evaluated based on the measured initial concentration. Thus, a 48 h EC50=0.134 mg/L (recalculated measured initial concentration) has to be taken into account for assessment. The testing/validity criteria laid down in the OECD guideline 202 were fulfilled.

These findings are supported by a study conducted according to ISO 6341 15 (Water quality - Determination of the Inhibition of the Mobility of Daphnia magna Straus (Cladocera, Crustacea)) and in a study conducted according to DIN 38412, Part II 'Daphnia short-time test' (comparable to OECD Guideline 202 'Daphnia sp. Acute Immobilisation Test'). The 48 h EC50 values were 0.13 mg/L nominal (ISO 6341 15; mean of two tests) and 0.29 mg/L nominal (DIN 38412, Part II). The very high acute toxicity of hydroquinone to Daphnia magna (24 h LC50=0.09 mg/L nominal) found in another study conducted comparable to the German DIN 38412, Part II in 1977 could not be confirmed in the aforementioned guideline studies and is not considered further.

Long-term toxicity to aquatic invertebrates

The long-term toxicity of hydroquinone was investigated in a study conducted under GLP according to OECD Guideline 211 (Daphnia magna Reproduction Test). Daphnids were exposed to measured concentrations of 0 (control), 0.0029, 0.0049, 0.014, 0.039, and 0.076 mg/L for 21 d under semi-static conditions. The test concentrations were monitored via HPLC/UV. Effect parameters observed were inhibition of reproduction, cumulative number of surviving offspring, first day of birth, death and body length of parent daphnias, occurrence of aborted eggs and male individuals. The 21 d LC50 for parental daphnias was calculated to be 0.061 mg/L based on mean measured concentrations. The calculated 21 d EC50, NOEC and LOEC for inhibition of reproduction were calculated to be 0.080, 0.0029, and 0.0049 mg/L based on mean measured concentrations. Provided that the formed degradation products are also of high ecotoxicity the evaluation of the test based on the concentration of the parent compound alone may overestimate its toxicity. Provided further that the total amount of toxic equivalents is stable during the exposure period the initial concentration is regarded as relevant concentration. Therefore, the daphnia test was re-evaluated based on the measured initial concentration. Thus, a 21 d NOEC=0.0057 mg/L based on recalculated measured initial concentration was found. The testing/validity criteria laid down in the OECD guideline 211 are fulfilled

Toxicity to aquatic algae and cyanobacteria

The toxicity of hydroquinone to algae was investigated in a study conducted equivalent or similar to OECD Guideline 201 (Alga, Growth Inhibition Test). Cultures of Pseudokirchnerella subcapitata were exposed to measured concentrations (0-72 h geom. mean) of 0.0057, 0.018, 0.056, 0.11, 0.24, 0.45 mg/L and 0.00085, 0.0015, and 0.0033 mg/L (additional test) for 72 h under static conditions. The test substance concentrations were monitored by HPLC/UV. As a result of measuring the concentration after 72 h, the 0.04 mg/L test concentration was below the lower LOQ. Therefore, the decrease of concentration with time was determined using an initial nominal concentration of 0.63 mg/L. Based on the decay curve, concentrations below the LOQ were calculated. The 72 h NOEC and EC50 (growth rate each) were determined to be 0.0015 mg/L and 0.053 mg/L, respectively. Provided that the formed degradation products are also of high ecotoxicity the evaluation of the test based on the concentration of the parent compound alone may overestimate its toxicity. Provided further that the total amount of toxic equivalents is stable during the exposure period the initial concentration is regarded as relevant concentration. Therefore, the algal test is re-evaluated based on the measured initial concentration. The 72 h ErC50 and NOEC (growth rate) were determined to be 0.330 mg/L and 0.019 mg/L (based on recalculated measured initial concentrations). The 72 h EyC50 and NOEC (yield) were determined to be 0.041 mg/L and 0.085* mg/L (based on recalculated measured initial concentrations). The validity criteria according to OECD Guideline 201 were fulfilled.

Toxicity to aquatic plants other than algae

The effects of hydroquinone on photosynthetically active aquatic organisms were assessed using freshwater algae (see above). As stated in REACH Annex VII, for the assessment of effects on aquatic plants algae are preferred. Therefore, no studies with aquatic macrophytes were conducted.

Toxicity to microorganisms

The respiration inhibition of activated sludge was investigated using a scanning respirometer. A luminescence-based scanning respirometer, using a ruthenium (II) complex as the oxygen-sensing element, was employed to monitor the toxicity of phenolic chemicals to activated sludge. The ruthenium (II) complex was irradiated with an excitation light source and the resulting light emission was then sensed and transmitted by an optical fiber connected to a photomultipler tube. The light intensities sensed at a specific wavelength could be related to the dissolved oxygen concentrations in the samples. The 2 h IC50 was determined to be 71 mg/L (nominal).

The toxicity of hydroquinone to Pseudomonas putida was determined by measuring the cell multiplication inhibition. The cultures were inoculated at 25°C for 16 h under static conditions. The concentration of the bacterial suspension was measured turbidimetrically. A 16 h TT (EC3)=58 mg/L nominal was obtained.

The toxicity of hydroquinone to Microcystis aeruginosa was investigated by determining the cell multiplication inhibition threshold concentration. The cultures of M. aeruginosa were exposed to hydroquinone for 8 d under static conditions. The concentration of the algal suspension was determined turbidimetrically. A 8 d TT (EC3)=1 mg/L nominal was found.

Toxicity to other aquatic organisms

The effects of hydroquinone were assessed on representative organisms of the aquatic trophic web (destruents, primary producers, first and second order consumers). Therefore, no studies with other aquatic organisms than microorganisms, fish, daphnids and algae were conducted.

Toxicity to sediment organisms

In accordance with column 2 of REACH Annex IX, the toxicity to sediment organisms does not need to be investigated as direct and indirect exposure of the sediment compartment is unlikely. For substances being considered as „readily biodegradable“, it can be assumed that they will be almost completely biologically degraded within the STP process. Furthermore, for substances not passing the STP-process but being readily biodegradable, it can be assumed that they will be also biological degraded in the surface water within a short time. Furthermore, the substance is known to de unstable in water, it shows low adsorptive properties (log Koc = 9 L/kg) as well as a low bioaccumulative potential (log Kow = 0.59) .

Therefore, no tests on sediment organisms are required and the risk assessment is based on the equilibrium partitioning method.