EPA Siloxane Monitoring Proposal

September 6, 2012

The agency has reviewed the proposed environmental monitoring program for certain siloxanes (D4 and 

D5) as submitted by the Silicones Environmental Health and Safety Council on March 1, 2012 and 

related information provided to the agency on August 3, 2012. The agency generally agrees with SEHSCs 

environmental monitoring proposal for direct discharge sites. The agency has determined, particularly 

with respect to indirect discharge sites and publically owned treatment works, the proposal would not 

provide adequate information for the agency to conduct a risk assessment. Below is the agency’s 

position on what would constitute an adequate siloxane environmental monitoring program. 

1. Industrial Sites with Onsite Wastewater Treatment (Direct Discharge Sites)

The Agency agrees with SEHSC that all 4 SEHSC member direct discharge sites would be monitored as 

originally proposed by SEHSC. These sites are SEHSC member sites, most of which are manufacturing 

siloxanes and some also process siloxanes and/or formulate products containing siloxanes. 

2. Industrial Sites Discharging Wastewater to POTWs (Indirect Discharge Sites)

These are SEHSC member sites that process siloxanes and formulate products containing siloxanes. The 

SEHSC proposal did not include monitoring at these sites. Monitoring data from these sites would be 

used to characterize potential releases of siloxanes from hundreds of processing and formulating sites, 

including sites of non-SEHSC members. 

There are a total of 9 SEHSC indirect discharge sites. EPA believes that of the 9 sites, only five sites 

should be monitored because information has been provided to the Agency that indicates that three 

sites have no releases to water and one site that discharges wastewater to a tertiary treatment site

(these circumstances must be confirmed by SEHSC). Tertiary treatment is not a commonly used 

treatment method at POTWs and therefore monitoring at this site is not essential to this effort.

3. Publicly Owned Treatment Works (POTWs)

SEHSC has proposed environmental monitoring at 5 sites. SEHSC’s proposal only includes monitoring of 

theoretical worst case siloxane release scenarios versus providing a range of POTWs that would provide 

a range of release scenarios. The agency has concluded that 5 sites are insufficient to conduct a risk 

assessment because it is too small of a sample to characterize the impact of critical factors (population 

served by the POTW; treatment method used by the POTW; flow rate of the receiving stream) on 

releases and environmental concentrations of siloxanes from U.S. POTWs. SEHSC’s proposal to monitor

only 5 POTWs using 4 different treatment methods would be considered by many to be anecdotal. The 

agency’s position is that the number and range of POTWs that would be monitored must be able to 

account for the uncertainty and variability of these critical factors. EPA believes that monitoring at 16 

carefully selected POTWs could adequately address these critical factors. This would result in data 

which could be used to characterize a range of POTWs in a risk assessment of desired quality. 
EPA believes that monitoring developed by this Enforceable Consent Agreement (ECA) should support a 

risk assessment that will allow EPA to make a determination on whether or not risk management action 

is needed to address the release of siloxanes into the environment. Monitoring focused on evaluating a 

theoretical "worst case" with the implication that additional steps would be required to generate yet 

more data if such a worst-case assessment indicated greater than negligible risk, is not an approach EPA 

believes would be efficient and effective for this ECA.

While data from Wang et al. (2010) of D4 and D5 in effluent and sediment from POTWs in Canada is 

informative, it is likely that the Canadian sites are not representative of US POTWs. The study’s focus on 

lagoons is not consistent with wastewater treatment in the U.S. In addition the details of the locations 

and conditions of monitoring are not available because they are considered confidential. Finally, biota 

was not monitored in this study. Thus the Canadian data may have limited utility for EPA risk 

assessment purposes.

Key factors that are critical in choosing the number and type of POTWs because they likely impact the 

releases of siloxanes from POTWs are:

Population served by the POTW A POTW that serves a large population yet has a low influent 

flow would theoretically result in a worst case (i.e. the greatest mass and highest 

concentrations of siloxanes are being fed to the POTW). Similarly, a POTW serving a small 

population but receiving a large influent flow would represent a best case (i.e. smallest mass 

and lowest concentrations of siloxanes are being fed to the POTW).

Treatment method used in the POTW Activated sludge is the method used treat about 80% of 

the volume of waste water across the country. Lagoons are a common treatment method but 

generally serve smaller communities. There are additional treatment methods used even less 

frequently which are not a focus of this effort.

Flow Rate of the Receiving Water Body The amount of dilution provided by the receiving water 

body could impact concentrations of siloxanes in water and sediment.

Additional factors of interest for the monitoring effort are:

Organic Content of the Receiving Water Body Siloxanes are believed to partition preferentially 

to solids. EPA understands that it would be difficult to identify POTWs for potential monitoring 

based on this factor, but there would be value in sampling at several POTWs that discharge to a 

receiving water body with high organic content.

Geography Environmental conditions in different parts of the country could affect the 

partitioning and sedimentation of siloxanes due to the varying nature of watersheds and 

temperature variations can affect partitioning both during and after treatment.
The sampling plan matrix shown below is intended to result in a practical and efficient strategy for the 

monitoring of a range of possible POTW operations taking into account the factors noted above. This 

sampling proposal calls for monitoring at 12 POTWs and 4 lagoons.

 Low Population High Population

 High POTW Flow Low POTW Flow

Low Dilution

Act. Sludge

and

Lagoon

Act. Sludge Act. Sludge Act. Sludge

and

Lagoon

Act. Sludge Act. Sludge Act. Sludge Act. Sludge

Act. Sludge

and

Lagoon

Act. Sludge Act. Sludge Act. Sludge

and

Lagoon

High Dilution

High dilution in the above tables means the flow rate of the water body receiving the POTW 

effluent is much greater than the POTW influent flow rate.

Organic content of receiving stream should be monitored.

Facilities sampled should be from a variety of locations across the country.

All monitored POTWs should have a low industrial contribution to influent (<10%). This would 

allow an understanding of how the use of siloxanes in personal care products (vs. from industrial 

sources) contributes to their presence in the environment. Also, other sources of industrial 

waste water could impact a POTW’s ability to treat siloxanes.

Sampling Details for all Monitored Sites

2 sampling events from each site.

Media sampled will include POTW influent, effluent, biosolids, sediment at outfall, surface 

water. For the direct and indirect discharge sites, influent and effluent from on-site pretreatment 

and treatment systems, if applicable, would also be monitored.

Air sampling at one covered site as proposed by SEHSC.

Biota sampling: Benthic and multiple fish species at all SEHSC direct and indirect discharge sites 

provided there are sufficient biota present to monitor. EPA believes that monitoring from all 

these sites is needed to develop a data set for assessment that is better than anecdotal quality. 

The original SEHSC proposal called for biota monitoring at 4 direct discharge sites and 5 POTWs.