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EC number: 231-131-3
CAS number: 7440-22-4
There is a paucity of monitoring data for silver in freshwater
environments in Europe. There are several reasons for this, including
the relatively low levels of silver in the aquatic environment and the
requirement for commensurately low levels of detection (<100 ng/L),
which are generally not routinely achieved in analytical laboratories.
This means that in order to quantify exposure or characterise risk
reliably under either REACH (Registration, Evaluation, Authorisation and
restriction of CHemicals)
or the Water Framework Directive (WFD),
there needs to be a broad monitoring programme of regional background
concentrations of silver, and targeted, local investigations of
emissions of silver from manufacturing and downstream use processes.
This report describes the scope, results and implications of an
aquatic monitoring programme designed to establish:
background level of exposure to silver in the freshwater environment of
England and Wales (regional surface water monitoring).
of silver to the freshwater environment from wastewater treatment in
England and Wales, principally from domestic sewage treatment (regional
worst case” releases of silver to the freshwater environment from five
silver manufacturers and downstream users in England and Wales (local
The programme was designed to provide data to fulfil key
requirements of both REACH and the WFD. The range of silver
manufacturers and downstream users operating in England and Wales, as
well as the tonnages of silver handled annually, are considered to be
broadly typical of those found across wider continental Europe.
Therefore, the silver exposures observed by monitoring freshwaters in
England and Wales are considered to be directly relevant to exposures
across the European Union.
A total of 425 separate analytical determinations for dissolved
silver from 84 monitoring stations were carried out as part of the
regional surface water monitoring programme. Of these, 346 samples
(~80%) were reported as having dissolved silver concentrations below the
limit of quantification (6.6 ng/L) and of these, 280 samples (~65% of
all samples) were reported as below the limit of detection (3 ng/L).
Mean dissolved silver was measured below the analytical limit of
quantification (6.6 ng/L) at 54 of the 84 regional surface water
monitoring stations (64%). None of the mean dissolved silver
measurements in surface waters exceeded the freshwater Predicted No
Effect Concentration (PNEC) of 40 ng/L, either when directly compared to
the PNEC (face-value compliance) or when the variability of individual
measurements used to calculate the mean was also taken into account to
determine compliance statistically (probability of failure). Following
the exclusion of three sites which were considered likely to have
unidentified local silver emissions the mean of the maximum dissolved
silver concentrations reported at each station (the regional background
concentration calculated according to REACH guidance) was calculated as
6.1 ng/Lusing a statistical extrapolation technique to account for the
high level of censorship in the dataset. The maximum mean dissolved
silver concentration recorded at a station was 19.8 ng/L, or 16.8 ng/L
following exclusion of sites which were considered to have unidentified
local silver emissions.
The maximum mean concentration of dissolved silver measured in
sewage treatment effluents from regional effluent monitoring was 50.0
ng/L. The 90th percentile of mean dissolved silver in treated
sewage effluents was 32.9 ng/L. It should be noted that these
measurements are from the effluents and do not take into account any
dilution in the receiving environment. Dissolved silver was reported as
below the limit of quantification in all the landfill leachates sampled
and in the single mine water discharge. Effluent data were not used for
regional background concentration calculations.
The monitoring of dissolved silver at specific sites (local
exposure monitoring) suggests that potential risks (as defined by a
PEC/PNEC ratio in the receiving environment greater than one) due to the
manufacture or use of silver can be expected in some cases. However,
dissolved silver concentrations were highly variable both within and
between the different sites, which reduces the confidence that risks
were statistically significant. The compliance situation at one of the
sites (Site A) may also be affected by other potential sources of silver
upstream, whilst compliance at Site C was complicated by an additional
source of silver to the sewage treatment works (STW). Exposure
assessment under REACH for Site C is likely to be most appropriately
achieved using modelled rather than measured concentrations of silver.
Where influent and effluent monitoring has been undertaken at STWs
serving either manufacturers or downstream users it appears that the
removal of silver during sewage treatment is generally high, although
this is not necessarily true in all cases. The mean silver removal at
the four STWs which were monitored in the site-specific programme was
59%, although the mean removal at individual sites ranged from 16% to
84%. This may be due to differences in treatment type at the different
sites. Given the generally limited amount of information on the removal
of silver during sewage treatment, this project provides valuable
additional information for the environmental exposure assessment of
silver under REACH.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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