If you’ve been involved with completing or reviewing a Massachusetts Water Resources Authority (MWRA) permit application recently, you may have wondered why the MWRA included an Addendum for Cooling Systems Anti-Corrosion Chemicals Information.
This application adendum requires that information including the following be provided.
- Type of cooling system present and if it is closed- or open-loop
- Chemicals used for corrosion inhibition, if they are molybdenum-based, and the amount used
- Blowdown flow and frequency
- Name and address of the supplier of the anti-corrosion chemicals and a copy of their Safety Data Sheet (SDS)
The MWRA is requiring additional information on cooling systems because of the elevated levels of molybdenum detected in solids collected from wastewater samples. The increased concentrations were found during periods of peak cooling system use.
Molybdenum is now one of the top five pollutants of most concern to the MWRA. It’s a metal that occurs naturally in soil, minerals, and water. It is also commonly used as a corrosion inhibitor. According to the MWRA, research has shown that most of the molybdenum discharged from residential, commercial, and industrial buildings comes from its use as a corrosion control agent in air conditioning cooling systems.
Aside from its commercial and industrial applications, Molybdenum is an essential nutrient. According to the Agency for Toxic Substances and Disease Registry (ATSDR), the nutritional requirement for adults is 45 µg/day (0.64 µg/kg/day). However, overexposure has been associated with metabolic changes, liver and kidney toxicity, as well as possible carcinogenic, reproductive, and developmental effects.
Exposure to molybdenum in the general population is almost entirely from dietary intake. Beans, cereal grains, and leafy vegetables in particular have been found to readily absorb this metal. Drinking water coming from sources close to areas with high molybdenum contamination from industrial effluents may also contain elevated concentrations.
Currently, the MWRA has not set a daily discharge limit for molybdenum. However, the Toxic Reduction and Control (TRAC) division has been working on a voluntary program with suppliers of corrosion control chemicals to substitute their products containing molybdenum with those that don’t.
Per the MWRA, to date this program has helped reduce molybdenum effluent levels by approximately 40%. According to their website, the benefit of this initiative is that TRAC can provide a more comprehensive approach to toxics control (using both regulatory and non-regulatory methods) to impact a greater number of sewer users in the MWRA service area.
For more information on molybdenum and other pollutants of high concern to the MWRA, or for assistance completing your MWRA permit application and cooling system addendum, please contact us.
This blog was written by Beth Graham, Safety Partners’ Director of Quality, Research, and Training.