Common decking and insulation pesticide is a honeybee-killer

James Vallette | January 14, 2016 | Materials

At very low concentrations, a chemical widely used to kill termites also harms honeybees, according to a new US Environmental Protection Agency (EPA) study.[1] The use of this pesticide, imidacloprid, in building materials has soared in recent years.[2]

Manufacturers incorporate imidacloprid into exterior products like polystyrene insulation, vinyl siding, adhesives, sealants, and pressure-treated wood decking. Imidacloprid migrates from exterior building materials into water and soil. Bees also use sawdust to help build their hives. Beekeepers use treated wood for stands and treated insulation for nucs. But EPA’s bee research on neonicotinoids like imidacloprid has ignored the potential contribution of these materials. Instead, the agency has approved an ever-expanding list of building products in which it may be used.

Honeybee populations are plummeting. Nationwide, bee colony loss exceeded 40% between April 2014 and April 2015. In some states, beekeepers lost over 60% of their colonies.[3] A growing body of evidence points to imidacloprid as an accomplice. A closer look at the implications of its use in building materials is long overdue.

Registered Uses in Building Products

The EPA first registered imidacloprid for use as an agricultural pesticide in the United States in 1994.[4] In 2001, Bayer obtained the first EPA registration to use the chemical in treated wood and other building materials, under the trade name Preventol TM.[5]

Its use in pressure treated wood grew as manufacturers phased out chromated copper arsenate (CCA) formulations.[6] Beginning in 2002, mixtures of imidacloprid with fungicides became popular replacements for CCA.[7] Today, at least six manufacturers are registered to sell imidacloprid formulations for use in pressure treated woods, including Lanxess (which spun off from Bayer in 2004[8]), Arch Treatment Technologies, United Phosphorus, Viance, Willowood, and Zelam.

The EPA continued approving expansions of this pesticide’s use over the past decade, even as evidence of its harm to bees has increased.[9] In 2007, the EPA registered Lanxess’ Preventol® TM-CE 25 pesticide for use in composite woods like plywood and in plastics like polyvinyl chloride siding.[10] In 2011, Lanxess obtained EPA approval to use imidacloprid in expanded polystyrene foam, in a highly concentrated formulation named Preventol TM-EPS.[11] And in 2014, the EPA approved using it in adhesives and sealants.[12]

Concentrations of Harm

Unfortunately, it seems honeybees are attracted to that which poisons them. In May 2015, scientists reported in Nature that honeybees prefer nectar laced with neonicotinoids (particularly imidacloprid and thiamethoxam) to plain sucrose. “Free-flying honeybees prefer to collect sucrose solutions containing low concentrations of nicotine,” they found. “Remarkably, the preference occurred even when bees consuming these solutions were more likely to die.”[13]

The new EPA study classifies imidacloprid “as very highly toxic to adult honey bees” at very low levels of exposure. “The level of imidacloprid in nectar at or below which no effects would be expected to the colony is determined to be 25 micrograms per liter,” or 0.025 parts per million (25 parts per billion), the agency concluded.[14]

Building products can contain, relative to this tiny threshold, a lot of imidacloprid. At minimum, treated solid wood must retain 11 parts per million (ppm) imidacloprid to be effective, according to Viance.[15] Lanxess suggests the use of up to 300 ppm in wood surface treatments.[16] Composite woods like particleboard, OSB, and plywood can contain over 150 ppm imidacloprid.[17] Expanded polystyrene insulation commonly contains 200 ppm (0.02% by weight) imidacloprid.[18] Adhesives and sealants can contain up to 1,200 ppm (0.12%).[19] And plastics like PVC siding can contain 10,000 ppm (1% by weight)[20] – a concentration 400,000 times higher than what EPA determined is toxic to bees in nectar.


Pathways for exposure

There are many pathways for building materials to contribute to bees’ demise.

The impacts can start during construction: Bees produce glues – called propolis -- from sawdust and other wood sources to fill crevices and seal and varnish honeycombs.[21]

After construction is over, pressure treated wood manufacturers acknowledge treatments can leach from their products into the soil and water.[22]

“Some preservative may migrate from the treated wood into soil/water,” warns the label for NexWood’s “Water Repellent Stabilized Wood.” NexWood is a pressure treated wood containing imidacloprid.[23]

Bees may encounter imidacloprid as they forage in standing pools of water.[24]

In soil, plant roots draw in the imidacloprid, which winds up in pollen and nectar consumed by bees. Imidacloprid typically persists in soil until plants take it up, according to the EPA. It explains, “Imidacloprid is a xylem-mobile systemic compound that is readily taken up by the roots of the plant and translocated throughout the plant via the transpiration stream.”[25]


Beekeepers unintentionally may be bringing imidacloprid into the stands and nucs they build for bee colonies. They often use polystyrene insulation as nucs (boxes that hold honeybee colonies), as I noted in a Signal post last year.[26] Apiarists also use pressure treated wood for stands that hold the nucs.[27]

The EPA has not considered these exposure pathways from building materials to bees. The bees risk assessment report released this month does not mention building materials at all.[28] Maybe it’s worth a look now that the agency has found impacts at such a low concentration.


A deck builder recently told a trade magazine, “I don’t ask what’s in it, and I don’t know who makes it. I go to the lumberyard and ask, ‘You got any treated wood? What’s the price?’”[29]

Perhaps honeybees are today’s canaries in the coalmine, leading indicators that something is awry.[30] Cheap materials like treated building products mirror modern agricultural practices. They introduce substances that otherwise would not be present in natural systems. Product choices have consequences.

Simpler options abound in the natural world, that are healthy and create more jobs. Organic agriculture is a leading growth industry in my home state of Maine.[31] When the European Commission banned the use of imidacloprid and other neonicotinoids on flowering plants in 2013, it questioned whether these chemicals have any place in sustainable agriculture.[32]

The same question may be asked of the building and construction industry: why not consider naturally pest-resistant materials, like FSC-certified ipe, white oak, redwood, or cedar,[33] rather than pesticide-soaked wood and plastics for decking and siding? If such options are cost-prohibitive, it is only because market prices have not incorporated environmental consequences such as the decline in honeybees.

Thanks to Sarah Lott, Susan Sabella, Jon Stavis and Peter Sullivan for their assistance with this article. Bees in sawdust photo courtesy of Chris Harvey, Teakwood Organics LLC.

ToxServices just released a new GreenScreen assessment for imidacloprid, commissioned by the Natural Resources Defense Council.  It is now available on Pharos here. According to the GreenScreen, imidacloprid is known to be neurotoxic in man, very ecotoxic to aquatic and terrestrial organisms, and very ecotoxic in the soil environment.

[1]  Housenger, Justin. Memorandum. “Preliminary Pollinator Assessment to Support the Registration Review of Imidacloprid” [memorandum], US Environmental Protection Agency, January 4, 2016.!documentDetail;D=EPA-HQ-OPP-2008-0844-0140.

[2] The EPA Finally Admitted That the World’s Most Popular Pesticide Kills bees—20 Years Too Late.” Mother Jones. Accessed January 13, 2016.; see also Simon-Delso, Noa, Vanessa Amaral-Rogers, Luc P. Belzunces, Jean-Marc Bonmatin, Madeleine Chagnon, Craig Downs, Lorenzo Furlan et al. "Systemic insecticides (neonicotinoids and fipronil): trends, uses, mode of action and metabolites." Environmental Science and Pollution Research 22, no. 1 (2014): 5-34.

[3] “U.S. Beekeepers Lost 40 Percent of Bees in 2014-15.” ScienceDaily. May 13, 2015. Accessed January 14, 2016.

[4] “Notice Of Pesticide Registration [imidacloprid],” March 18, 1994. US Environmental Protection Agency, March 18, 1994.

[5] “Notice Of Pesticide Registration (Preventol TM Insecticide).” US Environmental Protection Agency, May 21, 2001.

[6] Walsh, Bill. “Removing Arsenic from Building Materials: A Success Story.” Healthy Building News. March 12, 2013.

[7] Peterson Wood Treating. “Wolmanized L3 Outdoor Wood” [pamphlet], 2007. ;  Roberts, Tristan. “New Treated Wood Uses Nonmetallic Biocides.” BuildingGreenMarch 2007.

[8] Lanxess Corp. "History - LANXESS.” Accessed January 13, 2016.

[9] The first reports of bee deaths caused by imidacloprid came shortly after the pesticide entered commerce in the early 1990s. See Bonmatin, J. M., I. Moineau, R. Charvet, C. Fleche, M. E. Colin, and E. R. Bengsch. "A LC/APCI-MS/MS Method for Analysis of Imidacloprid in Soils, in Plants, and in Pollens." Analytical Chemistry 75, no. 9 (2003): 2027-2033.'Imidacloprid%20Analysis%20in%20Soils,%20Plants%20and%20Pollen.pdf

[10] “Notice Of Pesticide Registration (Preventol Insecticide),” May 21, 2001. ; Lanxess Corp. “LANXESS Earns EPA Registrations for Imidacloprid Product Line,” September 28, 2007.

Example of vinyl siding using imidacloprid:

[11] Lanxess Corp. “LANXESS Corporation earns EPA approval for imidacloprid-based termiticide,” March 20, 2011. ; “Biocide Supplier Directory.” Coatings World, May 2011.

[12] Eagle, Venus. “Re: Label Amendment – Addition of use in adhesives and caulking Product Name: Preventol TM Preservative Insecticide” [memorandum]. US Environmental Agency, July 9, 2014.

[13] Kessler, Sébastien C., Erin Jo Tiedeken, Kerry L. Simcock, Sophie Derveau, Jessica Mitchell, Samantha Softley, Jane C. Stout, and Geraldine A. Wright. "Bees prefer foods containing neonicotinoid pesticides." Nature (2015).

[14] “The preliminary risk assessment identified a residue level for imidacloprid of 25 ppb, which sets a threshold above which effects on pollinator hives are likely to be seen, and at that level and below which effects are unlikely.” (“01/06/2016: EPA Releases the First of Four Preliminary Risk Assessments for Insecticides Potentially Harmful to Bees.”

[15] Viance’s label for EL2 One Pack states that “imidacloprid retention equivalent to or greater than 0.0003 Ibs. per cubic foot (pcf) (0.0048 kg/m3)… is the minimum retention level required for protection from subterranean termite attack ( According to the American Wood Council, the average density of softwood lumber is 433.57 kg/m3. (American Wood Council. “Environmental Product Declaration: North American Softwood Lumber,” April 16, 2013. On average, then, the “minimum retention level” required for imidacloprid in pressure treated softwood lumber is 11.07 ppm.

[16] Eagle, Venus. “Re: Label Amendment – Addition of Use in Adhesives and Caulking” [memorandum]. US Environmental Protection Agency, July 9, 2014.

[17] HBN calculations based upon dosage rates in Lanxess Corp. “Preventol Preservative Insecticide” [product label], May 19, 2010.  Wood density averages are provided in American Wood Council Environmental Product Declarations. (American Wood Council. “Environmental Product Declaration: Particleboard,” November 13, 2013.; American Wood Council. “Environmental Product Declaration: North American Oriented Strand Board,” April 16, 2013.; American Wood Council. “Environmental Product Declaration: North American Softwood Plywood,” April 16, 2013.

[18] “Imidacloprid.” Quartz. Accessed January 13, 2016.

[19] Eagle, Venus. “Re: Label Amendment – Addition of Use in Adhesives and Caulking” [memorandum], UA Environmental Protection Agency, July 9, 2014.

[21] “Benefits Of Propolis.” The Warré Store, July 23, 2009. Accessed January 14, 2016.

[22] “Polystyrene Insulation: Does It Belong in a Green Building?” BuildingGreen. August 2009.

[23] Nexwood tear sheet. Nextwood Industries Limited, September 2014.

[24] “Honey Bees and Your Swimming Pool: Not a Good Mix.” USDA Agricultural Research Service, April 26, 2012. Accessed January 14, 2016.

[25] Housenger, Justin. Memorandum. “Preliminary Pollinator Assessment to Support the Registration Review of Imidacloprid” [memorandum], US Environmental Protection Agency, January 4, 2016.!documentDetail;D=EPA-HQ-OPP-2008-0844-0140.

[26] Jim Vallette. “Bees Need Healthy Buildings Too.” The Signal.

[27] See for example Simon, Ed. “Build A Hive Stand.” Bee Culture, October 2013. A 1984 study of various hives treated with wood preservatives detected rises in toxic content in bees, beeswax, and honey. “Five hives were used for each preservative treatment: copper naphthenate, copper 8-quinolinolate, pentachlorophenol (PCP), chromated copper arsenate (CCA), acid copper chromate (ACC), tributyltin oxide (TBTO), Forest Products Laboratory water repellent, and no treatment (control). Honey, beeswax, and honey bees were sampled periodically during two successive summers. Elevated levels of PCP and tin were found in bees and beeswax from hives treated with those preservatives. A detectable rise in copper content of honey was found in samples from hives treated with copper naphthenate. CCA treatment resulted in an increased arsenic content of bees from those hives. CCA, TBTO, and PCP treatments of beehives were associated with winter losses of colonies.”[Kalnins MA, Detroy BF; J Agric Food Chem 32 (5): 1176-80 (1984)]

[28] Housenger, Justin. Memorandum. “Preliminary Pollinator Assessment to Support the Registration Review of Imidacloprid” [memorandum]. US Environmental Protection Agency, January 4, 2016.!documentDetail;D=EPA-HQ-OPP-2008-0844-0140. Similarly, a 2007 human health assessment explicitly acknowledges that it chose not to consider imidacliprod “products used as preservatives for wood products, building materials, textiles and plastics.” (Cutchin, W. “Imidacloprid. Human Health Risk Assessment. Section 3 Requests for Uses on Peanut, Proso Millet, Pearl Millet, Oat, Kava, Globe Artichoke, Caneberries, Wild Raspberry, and Soybeans.” US Environmental Protection Agency, April 30, 2007.)

[29] “Treated Wood Update.” Professional Deck Builder. Accessed January 14, 2016.

[30] Imidacloprid also may be harm people: the European Food Safety Agency says low levels of exposure can harm the nervous systems of children. Imidiacliprod “may adversely affect the development of neurons and brain structures associated with functions such as learning and memory,” it concluded in 2013. According to the New York Times, Bayer “sharply disputed” this notion.

[31] Bangor Daily News Editorial Board. “Organic Farming: Maine’s Small Economic Bright Spot.” The Bangor Daily News.

[32] Jolly, David. “Pesticides Linked to Honeybee Deaths Pose More Risks, European Group Says.” The New York Times, April 8, 2015.

[33] “8 Rot-Resistant Woods for Your Outdoor Projects.” Houzz. Accessed January 14, 2016. ; and, “Choosing Rot Resistant Wood.” The Craftsman Blog, January 6, 2014.