Nonylphenol ethoxylates (NPEs) are being phased out of use by the U.S. dairy industry due to concerns raised by foreign dairy product importers, including the European Union (EU) and China.

NPE is found in many products and has generally been considered safe for humans. The levels typically found in raw milk are very low, but NPEs residues can be concentrated during milk processing.

Inexpensive screening tests have made testing of bulk tank milk and finished products quick, easy, affordable and increasingly common in foreign markets. Therefore, NPE use in the U.S. has become a market barrier to dairy product exports.

In the U.S., NPE is used as a wetting agent in a variety of products. The most important use in the dairy industry is as a surfactant in iodine teat dips. Generally, the higher the iodine content, the more NPE is added to the product to keep the iodine in suspension.

There are alternative surfactants that can be used in iodine teat dips, and manufacturers are moving toward removal of NPE from their product lines.


Dairy plants producing finished products and cooperatives marketing milk are thinking about NPEs and how they may affect access to markets now and in the future. Some cooperatives have notified their members that use of NPE-containing products should be discontinued.

If you receive one of these letters, what do you need to know about reducing bulk tank NPE levels? If you are currently being tested and have gone NPE-free but still have detectable bulk tank levels, what could be the cause?

Bulk tank NPE levels can vary widely. At Eastern Lab Services (ELS), we have tested dairies using NPE-iodine teat dip with results that range from below 100 parts per billion (ppb) to above 1,000 ppb. The NPE level in the bulk tank depends on udder prep procedures, individual employees and NPE content of products used.

Specific practices such as use of spray dip and incomplete wiping of teat dip after prep can obviously lead to higher levels. Other sources of NPEs may not be as obvious or easy to eliminate as teat dip.

Simply switching to NPE-free teat dip has not been enough to immediately lower bulk tank NPE levels to below detectable on some farms. Tests, such as the ELISA test for NPE, are very accurate down to 20 ppb and can detect levels as low as 10 ppb.

For a reference, 1 ppb is equivalent to one drop of water in an Olympic-sized swimming pool. In addition to the test being very sensitive, NPEs may persist in a dairy system or be coming from sources other than teat dip.

Household laundry detergent has been NPE-free for many years, but commercial laundry detergent manufacturers are only under an EPA voluntary reduction in NPE use. If you are using commercial detergent or using a towel service, laundry detergent is a potential source of bulk tank NPE.

Towels tested at ELS that were washed in detergent containing NPEs had very high levels of NPE in the towels (greater than 270,000 ppb). Even after three months of washing in NPE-free detergent, 20 to 30 percent of that NPE remained in the towel.

Previous research has suggested that washing can remove NPE from cloth quickly in some cases but that NPE may also persist for a long time depending on conditions.

Unfortunately, just tossing the towels and buying new ones may not immediately solve your NPE problems either. A recent study by a UK environmental agency found new textiles also can have extremely high levels of NPE at purchase.

In fact, new cotton textiles had between 3,300 and 1.8 million ppb NPE. So if you buy new towels, expect to wash them a few times (in household detergent) before NPE levels drop. While it doesn’t seem like towels alone could cause a problem, it is the number one issue we have seen in farms that have struggled to reduce their bulk tank NPE.

NPEs may also be in your rubber or plastic parts. Equipment such as teat-dip drums and totes, sprayer lines and equipment may be contaminated with NPE. This NPE can be absorbed in the plastic or rubber and may leach back out when NPE-free product is introduced.

Other dairy equipment parts may also cause problems. Gaskets, inflations, hoses and basically anything rubber or plastic that comes in contact with milk, may retain NPE. Used gaskets tested for NPE ranged from 20,000 ppb to upward of 60,000 ppb, while new gaskets only contained trace amounts.

Expect to replace many of your rubber parts if you start out with high-bulk tank NPE numbers. If you have time to get your levels down, you may just stick to your regular replacement schedule; just don’t become frustrated when your test levels fall abruptly but you have difficulty getting to less than 10 ppb.

It can be in your water. Surface waters are more likely to contain NPEs than deep wells. Surveys of municipal drinking water supplies commonly have shown trace levels of NPE; however, several dairies we have tested have had NPE levels well above the detectable limit. This NPE may get into the milk through washwater or ingestion by the cows.

While just switching teat dip has been enough for most facilities to eliminate NPEs, for some dairies it does take time for counts to come down. Bulk tank milk was tested from more than 230 dairies shipping to cooperatives trying to go NPE-free.

Some dairies were able to rapidly drop their bulk tank counts with several able to go from bulk tank values of more than 300 ppb to undetectable levels in as little as two weeks.

Others struggled to lower bulk tank concentrations. After 90 days of testing, 30 percent of dairies still had detectable NPE levels. Monthly testing was continued on the dairies, and by 180 days almost 90 percent were below 10 ppb.

As phasing out NPEs continues to become a necessity, be sure to consider all areas of your dairy for potential sources.  end mark

Hilary M. Sullivan is the laboratory operations manager with Eastern Lab Services. Email Hilary M. Sullivan.