The Optical Brightener Project

The Optical Brightener Project aims to detect failing septic systems in our Marstons Mills River watershed, the system that feeds the Three Bays. The project tests for the presence of optical brighteners in nearby waters, indicating ineffective natural cleansing of wastewater.

Optical brighteners are fluorescent white dyes that are added to almost all laundry detergents to help make clothes look brighter. Because these dyes are a component of laundry effluent, they are generally found in domestic waste water and can therefore enter the subsurface environment as a result of ineffective sewage treatment. Removal of the optical brightener dyes in groundwater is by adsorption onto soil and organic materials; in surface waters they are removed by adsorption and photo decay. Since adsorption is a critically important process in the performance of septic systems, the recovery of these dyes in nearby waters indicates ineffective natural cleansing of wastewater.

Because the optical brightener dye is fluorescent, it doesn't color the waterways. However, it does show up under black light when the dye is "captured" by unbleached cotton cloth left in our streams and rivulets. High fecal coliform counts without a positive reading for optical brighteners in the water is evidence that wildlife is a probable source of the fecal coliform. But when a water sample from a site in our streams shows a positive reading for optical brightener dye along with a high fecal coliform count in a water sample, then the likely source is a septic system which is not properly filtering the water before it enters the open stream beds.

The follow-up for failing septic systems in our Marstons Mills River watershed area is in the domain of Dr. Dale Saad, the Town of Barnstable's Coastal Health Coordinator who, in the interest of public health, can address the problem through the authority of her office.


The Ipswich Coastal Pollution Control Committee and the Gloucester Shellfish Department/Shellfish Advisory Commission have found that optical brightener testing, when done in combination with a larger sampling program, reliably helps identify faulty septic systems, storm drain cross-connections, and human/animal waste differentiation. These two organizations produced an Optical Brightener Handbook that can be used by other water quality monitoring groups.