Silver bromide

Monitoring data

Administrative data

Endpoint:

monitoring data

Type of information:

other: Environmental monitoring programme

Adequacy of study:

key study

Study period:

2009-2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Reliable study conducted in accordance with specified guidance.

Data source

Reference

Reference Type:

other: Monitoring program

Title:

Unnamed

Year:

2010

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

This report describes the scope, results and implications of an aquatic monitoring programme designed to establish:
1.   The background level of exposure to silver in the freshwater environment of England and Wales (regional surface water monitoring).
2.   Emissions of silver to the freshwater environment from wastewater treatment in England and Wales, principally from domestic sewage treatment (regional effluent monitoring).
3.   “Reasonable worst case” releases of silver to the freshwater environment from five silver manufacturers and downstream users in England and Wales (local exposure monitoring).
The programme was designed to provide data to fulfil key requirements of both REACH and the WFD

GLP compliance:

no

Type of measurement:

other: Background and natural background concentrations and concentration at contaminated sites

Media:

surface water

Test material

Test material information

Constituent 1

Reference substance name:

Silver

EC Number:

231-131-3

EC Name:

Silver

Cas Number:

7440-22-4

Molecular formula:

Ag

IUPAC Name:

Silver

Details on test material:

Monitoring program - no data reported

Study design

Details on sampling:

Full details of methodology provided in attached report

Results and discussion

Details on results:

A monitoring study of dissolved silver concentrations in surface waters in England and Wales. Monitoring was undertaken at 84 sites, although for 3 of these sites potential local impacts were identified. The calculation of regional background concentrations was therefore performed using the remaining 81 sites. The maximum silver concentration was All of the approaches to handing non-detected data provide similar estimates of the regional background concentration. The first approach is that recommended by the technical guidance (ECHA 2010), although statistical approaches which do not require a single arbitrary value to be assigned to values below either the LOD or LOQ are also recommended. The MLE and KM approaches are both examples of such methods. These approaches can be sensitive to the level of censorship in the dataset, and some methods perform better than others at high levels of censorship, as is the case here. The value of 6.1 ng/L derived using the KM approach is selected as the most robust value for a regional background concentration of dissolved silver in freshwaters because the approach used as it does not rely on substitution of censored data with a single value, and is more robust than the MLE approach at high levels of data censorship.

Applicant's summary and conclusion

Executive summary:

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)[1] or the Water Framework Directive (WFD)[2], 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:

1.   The background level of exposure to silver in the freshwater environment of England and Wales (regional surface water monitoring).

2.   Emissions of silver to the freshwater environment from wastewater treatment in England and Wales, principally from domestic sewage treatment (regional effluent monitoring).

3.   “Reasonable worst case” releases of silver to the freshwater environment from five silver manufacturers and downstream users in England and Wales (local exposure monitoring).

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 90^th 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.

[1]http://ec.europa.eu/environment/chemicals/reach/reach_intro.htm

[2]http://ec.europa.eu/environment/water/water-framework/index_en.html