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ENVIRONMENTAL EXPOSURE
Environmental fate
DBP may be released into the environment during its production and subsequent life cycle stages, including disposal. Emissions to water and air are expected to be the most important entry routes of DBP. General characteristics of DBP which are relevant for the exposure assessment are given below.
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Degradation
The contribution of hydrolysis to the overall environmental degradation of phthalate esters, including DBP, is expected to be low. Photo-oxidation by OH radicals contributes to the elimination of DBP from the atmosphere. An atmospheric half-life of about 1.8 days has been estimated for the photo-oxidation reaction. The metabolic pathway of aerobic and anaerobic biodegradation of phthalates can be summarised as follows. First the di-ester is hydrolysed into the mono-ester by esterases with low substrate specificity. Subsequently the mono-ester is converted into phthalic acid. There is ample evidence that DBP is ready biodegradable under aerobic conditions. The same literature sources indicate that biodegradation of DBP is much slower in the anaerobic environment, e.g. sediments or deeper soil or groundwater layers.
Distribution
The Henry's law constant of 0.27 Pa.m3/mol indicates that DBP will only slowly volatilize from surface waters, i.e. virtually all of the DBP will remain in the water phase at equilibrium.
The octanol/water partition coefficient (Kow) of DBP is high and consequently the equilibrium between water and organic carbon in soil or sediment will be very much in favour of the soil or sediment. A Koc of 6,340 l/kg can be calculated using the log Kow of 4.57. Despite its low volatility, DBP has been reported as particulate and as a vapour in the atmosphere. In the air DBP is transported and removed by both wet and dry deposition.
The high Kow of DBP indicates that the substance has a potential for bioaccumulation. However, the actual degree of bioaccumulation in vivo will be determined by the metabolisation and the elimination rate of the substance. The available BCF data demonstrate a relatively low bioconcentration, but also indicate that higher BCF values are obtained when the BCF is calculated for the total amount of metabolites using 14C-labelled material. The experimental BCF of 1.8 l/kg for DBP from the recent study is used in the further risk assessment for secondary poisoning (aquatic route). In the risk characterisation attention will be paid to the possible consequences of using a higher value. No experimental BCF data are available for terrestrial species. EUSES calculates a BCF worm of 13 kg/kg.
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Exposure scenarios
The environmental exposure assessment of DBP will be based on the expected releases of the substance during the following life cycle stages:
I. Production
II. Distribution (e.g. road transport)
IIIa. Processing in polymers
IIIb-1. Formulation in adhesives
IIIb-2. Processing/use of adhesives
IIIc-1. Formulation in printing inks
IIIc-2. Processing/use of printing inks
IIId. Processing of glass fibres
IIIe. Processing of grouting agents
IV. Exterior use of DBP containing products
V. Incineration and disposal of DBP containing products.
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For most of these life cycle stages local Predicted Environmental Concentrations (PECs) were calculated based on either generic (TGD defaults) or site-specific scenarios. Results are presented in Table 3.1 and Table 3.2 for production and processing, respectively. Regional PECS are calculated to be 0.4 µg/l for water, 89 µg/kg for sediment, 0.006 µg/m3 for air and 0.01 mg/kg for soil.
In addition to these estimated PECs also a number of EU monitoring data are available for DBP in various environmental compartments (mainly water and sediment).
Table 3.1 Local PECs in the various environmental compartments at production
Table 3.2 Local PECs in the various environmental compartments at formulation/processing
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EFFECTS ASSESSMENT
Aquatic compartment
Both short-term and long-term aquatic toxicity data are available for DBP. The Predicted No Effect Concentration for the aquatic compartment is derived from the 99-day NOEC of 100 µg/l for Onchorhynchus mykiss. This key study is supported by the Gammarus pulex study in which a similar value was found based on a decrease in the locomotor activity. An assessment factor of 10 will be used for the extrapolation. This factor is used because long term NOECs for three trophic levels are available. The PNEC aquatic amounts to 10 µg/l.
As there are no valid experimental data for the toxicity of DBP to sediment-dwelling organisms, the equilibrium method is used for the derivation of a PNEC in sediment: PNECsediment = 1.2 mg/kg wwt.
The test with the protozoan Tetrahymena pyriformis can be used to derive a PNEC microorganism. Applying a factor 10 on the EC50 of T. pyriformis leads to a PNEC value of 0.22 mg/l. It is realised that this PNEC is low compared to the fact that no biodegradation impairment of DBP was found at concentrations far above the water solubility.
Terrestrial compartment
The NOEC of 200 mg DBP/kg for Zea mays is used for the derivation of the PNEC for the terrestrial compartment. Applying an assessment factor of 100, results in a PNECterrestrial of 2 mg/kg dw. For comparison also a PNECterrestrial is derived based on equilibrium partitioning. This gives a value of 1.24 mg/kg dw, which is in agreement with the PNECterrestrial derived above.
Atmospheric compartment
There are a number of studies on the airborne toxicity of butyl phthalates to plants. In these studies, plants were exposed in a growth chamber or in a glasshouse to DBP vapour originating from plastics which contained DBP as a plasticizer or from substrates moistened with DBP. The results of the studies show a wide range of effect levels of butyl phthalates, ranging from 1.2 µg/m3 to 1,000 µg/m3. An average concentration of about 0.1 µg/m3 is considered to be a fairly good estimate of the plant NOEC for butyl phthalates. This NOEC of 0.1 µg/m3 DBP is currently used for the derivation of the PNEC for plants. Although the experiments were carried out under unfavourable greenhouse conditions and, additionally, the NOEC seems to be based on a very sensitive species, from a consistency point of view a factor of 10 is applied on the NOEC. This leads to a provisional PNECplant-air of 0.01 µg/m3. It was decided that further chronic testing was needed to establish a more reliable PNEC for plants exposed via air. It was agreed to perform a 3-4 months fumigation test with seven plant species (including Brassica).
Following the establishment of criteria for R54 (toxic to flora), application to DBP could also be considered.
Secondary poisoning
The overall oral LOAEL of 52 mg/kg bw for laboratory mammals is used for the derivation of the PNEC for predators (conversion factor = 20, assessment factor = 10), resulting in a PNECoral of 104 mg/kg in food.
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CHRONIC PLANT STUDY
Results
Visual injury was observed on all species, varying from chlorosis and necrosis, leaf crinkling to a total loss of colour in the leaves and needles. The variation in sensitivity between plant species was quantified on the basis of whole plant biomass (shoot plus root) in order to derive NOEC and EC10 values.
EC10 values for total biomass, including lower and upper limits, for six plant species
Interestingly, white clover was found to be more sensitive to DBP than cabbage. Further details can be found in the PRI (2002) report and IUCLID.
PNECplant-air proposal
The PRI (2002) study is considered acceptable and useful for deriving a PNECplant-air. Two different routes can be used for deriving the PNECplant-air: 1) the standard method (lowest NOEC/EC10 divided by assessment factor, and 2) statistical extrapolation with an additional assessment factor.
Using the lowest EC10 value, i.e. 0.33 µg/m3, and applying the standard factor of 10 would result in a PNECplant-air of 0.03 µg/m3. Calculating the 5th percentile of the species sensitivity distribution (EC10 values for effects on total biomass) would result in a median (50% confidence interval) value of 0.2 µg/m3 (ETX, 1993). The 5th percentile estimation meets the statistical goodness-of-fit requirements (Anderson-Darling test for normality). Calculating 5th percentile values for either root or shoot biomass, rather than total biomass, results in nearly the same 5th percentile.
The problem now is that there is no guidance yet on deriving a plant-air PNEC in the Technical Guidance Document (TGD) (EC, 2003b). The TGD focuses on the PNEC derivation for water, sediment and soil, but the assumptions etc. for those compartments may not directly hold for plants (airborne route). A number of considerations can be given here on the PNECplant-air derivation for DBP:
1. the focus is only on deriving a PNEC air for plants. This means that other taxonomic groups of the atmospheric compartment (e.g. insects) will remain beyond the scope of the PNEC. This implies that assessment factors may cover ‘less ecosystem’ than normally for water, soil and sediment.
2. the TGD (2003b) criteria for using statistical extrapolation are not all met here (e.g. number of NOECs), but they may also not be relevant here as the focus is only on plants (see point 1). There is a fairly well coverage of plant diversity in the selected plant species, and, in addition, an acceptable goodness-of-fit is shown. One may speculate then about the introduction of an additional assessment factor. Such additional assessment factor should still cover species diversity (see point 3). It is highly uncertain, however, whether a factor of 2, 3 or 4 should then be used. An arbitrary factor of 3 on the current 5th percentile would, for example, yield a PNEC of 0.07 µg/m3.
3. the focus in the tiered testing program, of which the PRI (2002) test is the last part, has been on sensitive species (Brassica in particular). This is supported by literature data. It should be noted, however, that the PRI (2002) test showed that white clover was even more sensitive than Brassica. Some factor is needed therefore for possible other, even more sensitive species than clover.
4. according to plant experts, the conditions in greenhouses, are very unfavourable to plants with respect to their sensitivity to toxicants. This due to optimal light and feeding conditions which optimise the exposure and therefore the toxicity. Therefore the standard factor of 10 for extrapolating from laboratory tests to the field-situation may be argued here (lower factor).
Taking all these points into consideration, it is clear that a quantitative approach on the PNEC derivation would be very difficult in this case. The standard assessment factor of 10 is most probably too high, but should it then be 4, 6 or 7.5? The same is true for the additional assessment factor on the 5th percentile. It is pragmatically proposed therefore to use a PNECplant-air of 0.1 µg/m3 for DBP in the revised risk assessment.
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RISK CHARACTERISATION
General discussion
Table 3.3 and Table 3.4 present the local PEC/PNEC ratios for, respectively, the production and processing stages of DBP. Details will be discussed in Sections 3.3.2 through 3.3.4.
Table 3.3 Local PEC/PNECs in the various compartments at production
Table 3.4 Local PEC/PNEC ratios at formulation/processing
Aquatic compartment (incl. sediment)
STP
The PNEC microorganisms for DBP was set at 220 µg/l. For the risk characterisation this value is compared with the PECSTP for the various exposure scenarios. For production and processing all PEC/PNEC ratios were found to be below 1 (conclusion (ii)).
The PNEC for surface water was set at 10 µg/l. For the risk characterisation this value is compared with the PEC in surface water for the various exposure scenarios. For production and processing all aquatic PEC/PNEC ratios were found to be below 1 (conclusion (ii)). It should be noted that for scenario IIIe grouting agent the PEC/PNEC based on the maximum (rather than 90 percentile) estimated PEC would amount to 1.5. The current scenario IIIe is based on a Norwegian case and extrapolation to other EU situations is difficult. The general conclusion, however, is that environmental releases of DBP during grouting activities may reach high levels in surface water. Therefore the environmental impact of these kinds of operations should be carefully assessed/monitored. Apart from a few rather old monotoring data (1984) the local and regional measured surface water concentrations were found to be below the PNEC (conclusion (ii)). The same is true for the calculated regional water concentration.
Sediment
The PNEC for sediment is 1.2 mg/kg wwt. As both the PNEC and the PEC were calculated with the equilibrium partitioning method from the water data, the same conclusions as for water can be drawn. In addition, most of the available monitoring data are lower than the PNEC for sediment-dwelling organisms. Only the upper limit of the Furtmann data (1993)4 for the river Lippe is higher than the PNEC (PEC/PNEC = 3). Recent marine sediment data (1997) in Denmark indicated that levels (maximum 2.4 mg/kg dwt) very close to the PNEC (fresh water based) can be found. Additional monitoring in marine sediments and identification of emission sources could be relevant. The PEC/PNEC ratio based on a calculated regional PEC sediment is 0.3 (conclusion (ii)).
Terrestrial compartment
The PNEC for the terrestrial compartment is 2 mg/kg dw. For the risk characterisation this value is compared with the PEC in soil for the various exposure scenarios. For production and processing all PEC/PNEC ratios were found to be below 1 (conclusion (ii)). Measured local data and the calculated regional PEC were also found to be below the PNEC (conclusion (ii)).
Atmospheric compartment
The provisional PNEC for the atmospheric compartment is 0.01 µg/m3. A comparison of this PNEC with the calculated and measured local (production and ormulation/processing) and regional PECs, shows that all PEC/PNEC ratios are above 1. A chronic fumigation test with plants has to be conducted (conclusion (i)).
Secondary poisoning
The PNECoral is 104 mg/kg. For the risk characterisation this value is compared with the PECs in fish and worm for the various exposure scenarios. All PEC/PNEC ratios were found to be far below 1 (conclusion (ii)). It should be noted that with the application of a higher BCF-value based on tests with 14C-labelled DBP, the risks for secondary poisoning would still be low.
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RESULTS FOR THE ENVIRONMENT - ADDENDUM
Conclusion (iii) There is a need for limiting the risks; risk reduction measures which are already being applied shall be taken into account.
This conclusion is reached because of anticipated risk for plants (atmospheric exposure) at a local scale for the DBP processing scenarios III-a (PVC production), III-b1 (adhesive production), III-c2 (printing ink usage) and III-d (glass fibre production).
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