Zinc specific points to be considered for integration into the INERIS report on Prioritisation of Substances under the Water Framework Directive
(Version July 2008)
Introduction
The WGe meeting of 15-16/10/08 agreed that industry could submit substance-specific points to INERIS for integration in the ongoing exercise on prioritisation of substances under the WFD, based on monitored data.The zinc Industry has taken into account points raised during the meeting, has revisited its original position paper and has now prepared some changes with new proposed solutions to its major points of concern which INERIS may find appropriate for inclusion in its study.
For each of these key points, we present the specific values proposed for change, with a short justification. To clarify, specific calculations for zinc are presented where appropriate. Since the risk-based prioritisation on monitored data refers to existing EU risk assessments (RA) as a primary source of information, we have also used the EU RA on zinc and 5 zinc compounds (Rapporteur country: The Netherlands, ECB 2008) as a general reference for the proposed changes[1].
The five key points related to the zinc analysis for which we are proposing changes for consideration can be summarised as:
- Selection of an appropriate PNECwater
- Use of total concentration data to calculate the PEC/PNEC ratiofor water
- Application of the added risk approach to the zinc data
- Selection of an appropriate PNECbiota
- Application of the biota scenario for an essential element such as zinc
The Zinc Industry is committed to working closely with the EU Institutions and other stakeholders in order to contribute effectively to better regulation.
Issue 1: PNECwater
-current value used:3.1 µg Zn/l (dissolved). This is the softwater PNECadd from the EU RA.
-proposed change: change thePNECwater value to 7.8 µg/l. This is the generic PNEC from the RA. This value is expressed on a dissolved zinc concentration basis. It is indeed a “PNECadd”, to be applied using the added risk approach (see issue 3).
-Justification:in the EU RA, the “softwaterPNEC” for zinc was explicitly developed only for use in the rare cases where water hardness is extremely low: “It is emphasised that the soft water PNECadd, aquatic will be applied only to waters with a low hardness, i.e. less than 24 mg/l (as CaCO3) and will not be used as a default value in case data on hardness are lacking; the use of the generic PNCadd, aquatic remains the starting point of the risk assessment” (quote from RA zinc, page 196, ECB 2008). Referring to this explicit wording in the RA, and considering that the monitoring-based prioritisation exercise is ageneral assessment of the European waters,it is proposed to use the generic PNEC from the RA, instead of the softwater PNEC. Generic PNECs in the EU RAs are developed for coverage of EU waters, including the realistic worst case. Furthermore, it is noted that this kind of special softwater PNEC is derived for zinc only, and not for other substances. Its use would thus not provide the same reference basis as for other substances.
-reference : EU risk assessment on zinc and 5 zinc compounds (ECB 2008)
Issue 2: The use of total concentration data for calculating the PEC/PNEC ratio for water
-currently, measured values of PECtotal and PECdissolved are both compared with the PNEC, which is expressed on a dissolved concentration basis.
-proposed changes:
a) calculate the risk ratio with PEC and PNEC both expressed on a comparable basis, i.e. both expressed as total or as dissolved zinc.
b) In this respect, it is proposed to use only the monitored total zinc concentrations in water as PEC, and not to use the measured dissolved concentrations.
c) To make the necessary conversions between the dissolved and the total zinc concentration, the generic Kp value for zinc from the RA should be applied, according to the formula from the TGD:
[Me]diss = [Me]total / 1+(Kp*Cs), where
-Kp: water-suspended matter partition coefficient for metal X (for zinc: 110000l/kg (EU RA))
-Cs = suspended matter concentration (TGD default: 15 mg/l)
This conversion can be applied on both PEC and PNEC. Calculated for zinc, this becomes:
- [Zn]diss = [Zn]total / 1 + (110000 l/kg * 0.000015g/l)
= [Zn]total / 2.65
- PNEC(expressed as total zinc) = 7,8 µg Zn/l (PNEC expressed as dissolved zinc) * 2.65
= 20.7 µg Zn/l
Justification:
In risk assessment, the PEC and PNEC used to calculate the risk ratio must be expressed on a same basis, i.e. either both expressed as total metal or as dissolved metal concentration.
In the current monitored-based prioritisation exercise, the measured total concentrations are by far the most extensive database, which provides the required coverage of the member states. In contrast to that(as also indicated during the WGe discussions), the measured dissolved concentrations for metals are not reliable, and cover only 2 member states. Moreover, the 90P value of the dissolved data is for zinc (as for other metals) higher than the 90P of the measured total concentrations, which suggests a problem with the relevancy of the dissolved data. For these reasons, it is proposed not to use the measured dissolved concentrations, but to use only the measured total concentrations.
In order to compare “like with like” for the risk ratio calculations, it is considered best to calculate the dissolved and total concentrations by using the partition coefficient, according to the TGD. For zinc, the Kp value of 110,000 l/kg is proposed, which is used throughout the RA to do the necessary conversions between total and dissolved concentrations. This Kp value followed from a consistent experimental database on EU waters (EU RA, ECB 2008). The Kp can be used for:
-calculatingthe PECdissolved from the PECtotal
-calculating the PNEC expressed on a total concentration basis from the PNEC expressed on a dissolved concentration basis.
reference : EU risk assessment on zinc and 5 zinc compounds (ECB 2008)
Issue 3: Application of the added risk approach on the zinc data (related to the PNECwater)
-currently, the added risk approach is not applied in the analysis.
-proposed change:apply the added risk approach for zinc, as is done in the RA. To this end, the natural zinc background is subtracted from the measured PEC, before calculating the PECadd/PNECadd ratios.
To do this, it is proposed to proceed as in the EU RA: abackground of 3 µg Zn/l (EU realistic worst case) and/or 12 µg Zn/l (average EU value; both are expressed as total zinc concentrations) is subtracted from the measured total concentrations of zinc in water. The resulting “PECadd” value can be compared to the PNECadd, if the latter however is also expressed on a total concentration basis. In order to do this, the generic PNECaddfrom the RA, which is set on a dissolved concentration basis, needs to be first transformed into a PNECaddexpressed as total, following the approach described under “issue 2”.
PECadd, total = PEC total (measured) – background
risk ratio is calculated as: PECadd, total/PNECadd, total. To make the ratio on a comparable basis, the PNECadd, dissolved needs first to be converted into the PNECadd, total, following the Kp approach (see issue 2).
For zinc, this would mean[2]:
-PEC2= 29µg Zn/l
This measured value includes the background (BG), so the PEC2add is calculated as:
- 29 – 3 = 26µg Zn/l (considering worst case background for EU waters)
- 29 – 12 = 17 µg Zn/l (considering the average background for EU waters)
-PNECadd, dissolved = 7,8 µg Zn/l
PNECadd, total = 7.8 * 2.65 = 20,7 µg Zn/l
PEC2add, total/PNECadd, total= 26/20,7 = 1,3 (worst case background correction)
PEC2add, total/PNECadd, total= 17/20.7 = 0,8 (average background correction)
Alternatively, the risk ratio can be calculated from PECadd/PNECadd both expressed on a dissolved concentration basis. In this case, the PNECadd from the risk assessment is taken as such (7.8 µg/l), and the PECadd, total is translated to PECadd,dissolved by applying the Kp dissolved-suspended matter from the RA:
PECadd, total = PEC total (measured) – background
PECadd, dissolved = PECadd, total/2,65
risk ratio: PECadd, dissolved/PNECadd, dissolved
The result is the same as with the PEC/PNEC based on total:
-PEC2add, total – BG= 26-17µg Zn/l (see above)
- PEC2add, dissolved= 26/2.65 = 10,4 µg Zn/l (considering worst case background for EU waters)
- PEC2add, dissolved = 17/2.65= 6,4 µg Zn/l (considering the average background for EU waters)
PEC2add, dissolved/PNECadd, dissolved= 10,4/7,8 = 1,3 (worst case BG correction)
PEC2add, dissolved/PNECadd, dissolved= 6,4/7,8 = 0,8 (average BG correction)
-Justification:In the EU RA on zinc, the “added risk approach” has been used to account for the variability of natural background concentrations of zinc over the different geographic regions. In that “added risk” approach, both PEC and PNEC are expressed on an “added to background” basis (PECadd/PNECadd). This is achieved by:
a) subtracting the zinc BG from the Zn concentrations in the ecotoxicity tests, and deriving the PNEC from these “NOECadd” values, and
b) by modelling the anthropogenic zinc emissions into a PECadd, or by measuring zinc concentrations in the water, and subtracting the natural background: “In case measured environmental concentrations are used in the risk characterisation, either the natural background concentration has to be subtracted from the measured environmental concentration (resulting in a traditional "PECadd / PNECadd"ratio) or the natural background concentration has to be added to the PNECadd (resulting in a traditional "PEC / PNEC" ratio)” (RA zinc, ECB 2008).
In the RA, the values of 3 µg Zn/l and 12µg Zn/l were used as background for EU waters, reflecting realistic worst case and average natural background, respectively, as following from extensive data on backgroundreported by the member states.
-reference : EU risk assessment on zinc and 5 zinc compounds (ECB 2008)
Issue 4: PNECbiota
-current PNECbiota:= 8,84. This value is calculated from the recommended daily zinc intake for human (10mg/d)
-proposed change:according to the outline of the prioritisation analysis, the PNECbiotashould be calculated from the acceptable daily intake (ADI) for zinc. The ADI for zinc is 50 mg/d (= 0,71 mg Zn/kg BW.d).
As such the “PNEC biota”for zinc is:
ADI (mgZn/kg food) = 0,1 * 0,71 mg Zn/kgBW.d * 70kg BW/0,115 (kgfood/d)
= 43,5 mg Zn/kg food
Justification:In the EU RA, a NOAEL of 50 mg Zn/d and a MOS of 1 were set, after extensive discussion of the available evidence: “For the risk characterisation, an overall oral NOAEL of 50 mg Zn2+/day (0.83 mg/kg bw/day) is set on the human volunteer study by Grand Forks (Davis et al. 2000; Milne et al., 2001). Given that this study was with women (the most sensitive population in zinc supplementation studies), and that in women clinical signs begin to appear only at a dose three times this NOAEL, a minimal MOS of 1 is considered sufficient when comparing the human NOAEL with the exposure levels for workers/consumers/general population”(RA ZnO, part: human health, ECB 2004, p.101). This NOAEL with MOS of 1 corresponds to the ”Acceptable daily intake” (ADI) considered in the prioritisation analysis, and should thus be used.
Reference: EU RA on ZnO, part: human health, ECB, 2004.
Issue 5: Application of the biota scenario for an essential element such as zinc
-Currently, a risk ratio for biota is calculated for zinc
-Proposal: it is proposed not to consider a biota scenario for the essential element zinc since it is not relevant, as was concluded in the zinc RA (2008).
Justification: On secondary poisoning, the EU RA concludes that “it is concluded that secondary poisoning is considered to be not relevant in the effect assessment of zinc. Major decision points for this conclusion are the following. The accumulation of zinc, an essential element, is regulated in animals of several taxonomic groups, for example in molluscs, crustaceans, fish and mammals. In mammals, one of the two target species for secondary poisoning, both the absorption of zinc from the diet and the excretion of zinc, are regulated. This allows mammals, within certain limits, to maintain their total body zinc level (whole body homeostasis) and to maintain physiologically required levels of zinc in their various tissues, both at low and high dietary zinc intakes. The results of field studies, in which relatively small differences were found in the zinc levels of small mammals from control and polluted sites, are in accordance with the homeostatic mechanism. These data indicate that the bioaccumulation potential of zinc in both herbivorous and carnivorous mammals will be low. Based on the above data, secondary poisoning and the related issues bioaccumulation and biomagnification are not further discussed in this report”. (RA Zn part: Environment, ECB 2008, page 292).
This conclusion of the RA reflects the fact that zinc is an essential element, needed for all life, from human beings to the microorganisms. The calculation of a risk ratio for zinc for prioritisation is therefore considered not relevant.
Regardless of this, the PNECbiota used by the prioritisation analysis is erroneously based on the recommended daily intake, and not on the acceptable daily intake, as it should be (see issue 4).
It is further emphasised that the monitoring database on biota zinc concentrations is very limited, and therefore not at all to be considered of the same relevancy for EU water quality as the one on total zinc concentrations. In conclusion, the biota endpoint should be omitted from the zinc analysis.
Reference: EU Risk assessment on zinc and 5 zinc compounds (ECB 2008)
[1]The comments made in this file reflect the best way to perform the monitored-based risk analysis according to the principles outlined in the EU RA (2008). Industry reserves its position that there are aspects of the RA on zinc that can be further refined as has also been concluded by the EU “Scientific Committee on Health and Environmental Risks” (SCHER 2007). Such refined elements could also be included in a risk-based prioritization.
[2]It is emphasized that the risk ratios calculated below do not include a correction for zinc bioavailability. Yet, the RA emphasized that such correction should be made in any risk analysis on zinc in water (RA zinc, “overall conclusions”). For the purpose of this general assessment of EU waters, an average bioavailability correction of e.g. 60 % could be applied (cfr. EU RA zinc, bioavailability factors in EU regional waters, table 3.4.69, p325).