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Not Ready for Roundup™ — The Regulation of Glyphosate Under California’s Proposition 65

March 8, 2016

Last September, the California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (“OEHHA”) issued a notice of its intent to list glyphosate as a chemical “known to the state” to cause cancer.[1] Listing glyphosate as a known carcinogen would subject the chemical to new consumer warnings and other requirements under California’s Safe Drinking Water and Toxic Enforcement Act of 1986, commonly known as Proposition 65.[2]

Glyphosate is one of the most widely-used herbicides in the United States. It was developed by the Monsanto Company in the 1970s and marketed under Monsanto’s well-known Roundup™ brand. For those reasons, it is no surprise that Monsanto (along with other agricultural chemical producers) has aggressively opposed OEHHA’s proposed listing decision. Most recently, Monsanto filed a petition for writ of mandate in California Superior Court (Fresno County) in an attempt to block the listing, arguing that the statutory basis underlying OEHHA’s action violates both the California and U.S. Constitutions.[3]

Monsanto’s lawsuit is significant for a number of reasons. It raises fundamental issues over how scientific health assessments can appropriately be used as the basis for governmental actions, with broad-reaching implications for both consumers and the overall economy. As a practical matter, it also challenges a key element of a unique California regulatory program that has now been in place for three full decades.

Proposition 65 Overview

Proposition 65 was enacted as a ballot initiative approved by California voters in 1986. It has two central provisions. The first is a prohibition against the contamination of sources of drinking water with chemicals known to the state to cause cancer or reproductive toxicity.[4] The second is a requirement that any person in the course of doing business must provide a clear and reasonable warning before exposing others to the same chemical carcinogens or reproductive toxicants.[5] The warning requirement is the one best known to the public, which for years now has seen Proposition 65 warnings covering gasoline sold at service stations, alcoholic beverages sold in bars and restaurants, cigarettes and other tobacco products, and a range of additional consumer goods.

By law, OEHHA is required to develop and regularly update a list of chemicals known to the state to cause cancer or reproductive toxicity for Proposition 65 purposes.[6] At a minimum, the statute requires that the list include chemicals identified as carcinogens under provisions of the California Labor Code that focus on workplace exposure to hazardous materials — this is sometimes referred to as the “Labor Code listing mechanism.”[7] The relevant Labor Code provisions in turn refer to actions taken by various other agencies to identify chemicals with carcinogenic effects.

Among the agencies referenced by the Labor Code is the International Agency for Research on Cancer (“IARC”). IARC is a specialized part of the United Nations’ World Health Organization that was created to promote cooperation on cancer research internationally.[8] IARC has developed a particularized classification scheme for categorizing chemicals based on their potential to cause cancer in humans and experimental animals. Under this scheme, a chemical can be classified as either: (Group 1) carcinogenic to humans; (Group 2A) probably carcinogenic to humans; or (Group 2B) possibly carcinogenic to humans.[9]

OEHHA’s practice of applying IARC’s classification scheme as part of the Labor Code listing mechanism has been tested repeatedly by the courts. In Styrene Information & Research Center v. Office of Environmental Health Hazard Assessment (“SIRC v. OEHHA”),[10] the trial court found that OEHHA could not rely simply on IARC to determine what constituted a chemical “known to the state” to cause cancer in the absence of sufficient evidence to support that determination, and the California Court of Appeal affirmed the trial court’s conclusion. According to the Court, the listing of a chemical using the Labor Code listing mechanism must always be supported by a finding that the chemical in fact is known to the state to cause cancer, whether that showing is provided by IARC or premised on some other source.[11]

IARC’s Assessment of Glyphosate and OEHHA’s Proposed Listing Determination

In March 2015, IARC issued Volume 112 of its Monographs on the Evaluation of Carcinogenicity Risks to Humans.[12] Volume 112 included a 92-page Monograph describing its assessment of the carcinogenicity of glyphosate.[13] The Monograph assessed that “[t]here is limited evidence in humans for the carcinogenicity of glyphosate,” noting that “[a] positive association has been observed for non-Hodgkin lymphoma.” It also assessed that “[t]here is sufficient evidence in experimental animals for the carcinogenicity of glyphosate.”

The Monograph concluded with an overall evaluation that glyphosate is “probably carcinogenic to humans (Group 2A),” noting that

In addition to limited evidence for the carcinogenicity of glyphosate in humans and sufficient evidence for the carcinogenicity of glyphosate in experimental animals, there is strong evidence the glyphosate can operate through … key characteristics of known human carcinogens and that these can be operative in humans.

In light of the issuance of IARC’s Monograph, OEHHA issued its notice of intent to list glyphosate using the Labor Code listing mechanism under Proposition 65 on September 4, 2015. In its website posting of the notice,[14] OEHHA stated that it would provide an opportunity to comment on the proposed listing, but noted that

Because these are ministerial listings, comments should be limited to whether IARC has identified the specific chemical or substance as a known or potential human or animal carcinogen. Under this listing mechanism, OEHHA cannot consider scientific arguments concerning the weight or quality of the evidence considered by IARC when it identified these chemicals and will not respond to such comments if they are submitted.

To date, OEHHA has received several thousand submitted comments, mostly from individuals and groups supporting the proposed listing, but also from Monsanto, other chemical producers, and industry groups opposing the listing. At this point, the public comment period is closed, and OEHHA has yet to take final agency action on the listing.

The Monsanto Litigation and the Impact of OEHHA’s Proposition 65 Implementing Regulations

Monsanto’s lawsuit seeks to enjoin OEHHA from taking action on the proposed glyphosate listing, based on a series of related claims that any such action would abrogate OEHHA’s independent administrative responsibilities under federal and state law. Monsanto asserts, among other things, that listing glyphosate as a carcinogen under Proposition 65’s Labor Code listing mechanism would improperly delegate “law-making authority to an unelected, undemocratic, unaccountable, and foreign body without providing intelligible principles or procedural safeguards to define the boundaries of that authority or prevent its arbitrary exercise,” in violation of Constitutional requirements protecting free speech, due process, the separation of powers, and even “the Guarantee Clause of the United States Constitution, which guarantees to the citizens of every state, including California, a ‘Republican Form of Government.’”

Notably, Monsanto does not allege that OEHHA’s proposed glyphosate listing violates Proposition 65. The validity of OEHHA’s continued use of the Labor Code listing mechanism has already been sustained by the courts for statutory purposes. In California Chamber of Commerce v. Brown,[15] the petitioners argued that the Labor Code listing mechanism was valid only as a means for developing the initial list of chemicals known to the state to cause cancer or reproductive toxicity when Proposition 65 was approved by the voters in 1986. Both the trial court and the state Court of Appeal rejected this argument.

The Court of Appeal found that “given the remedial purposes of Proposition 65 and the mandate that it be broadly construed, … the Labor Code reference method … continues to specify the minimum content of the Proposition 65 list as it is revised and republished.” In support of this conclusion, the Court noted that:

OEHHA has consistently and publicly interpreted the Labor Code reference method as applying to revisions of the Proposition 65 list. It has explained its reasons for doing so in formal responses to public comments on listing notifications, letters to members of the regulated community and in a public proposal for comments on a formal regulation explaining its interpretation of the process of identifying chemicals for listing under this method.

During the course of proceedings to develop a formal regulation consistent with applicable court decision, [16] OEHAA received extensive comments from a variety of sources, including the American Chemistry Council and the California Chamber of Commerce.[17] After a lengthy public review period and multiple iterations of possible regulatory language, OEHHA eventually issued its final regulation on July 6, 2015.[18]

OEHHA’s final regulation — Title 27, CCR Section 25904 — nominally requires the listing of chemicals classified by IARC as Group 1, Group 2A, or Group 2B carcinogens; however, it specifically provides that a “chemical or substance for which there is less than sufficient evidence of carcinogenicity in experimental animals and classified by IARC in Group 2B shall not be included on the list.”[19] The regulation also requires OEHHA to provide a 30 day public comment period on whether or not a chemical or substance has been properly identified by reference to the Labor Code listing mechanism.[20] The regulation states, however, that OEHHA “shall not consider comments related to the underlying scientific basis for classification of a chemical by IARC as causing cancer.”[21] Any comments submitted must be “restricted to whether the identification of the chemical or substance meets the requirements of this section.”[22]

What this means is not entirely clear. While the regulation precludes specific challenges to the scientific evidence supporting individual IARC classification decisions, it does not explicitly preclude consideration of other evidence that may independently be relevant to a Proposition 65 listing determination. For example, if there are conflicting scientific studies completed more recently than those used by IARC, or which apply different, scientifically legitimate methodologies, there is no reason why they should not be considered for Proposition 65 purposes — regardless of whether they support a particular IARC determination.

Put another way, an IARC Group 1 or 2A classification decision could create a presumption that a chemical must be listed as a known carcinogen under Proposition 65; however, court decisions construing the application of the Labor Code listing mechanism and similar provisions suggest that at least in some circumstances the presumption should be a rebuttable one. That is because, as the court noted in SIRC v. OEHHA,

… chemicals may be included on the Proposition 65 list only if there is a sufficient showing that they in fact cause cancer or reproductive toxicity. This interpretation is consistent with the legislative history underlying Proposition 65 and does not conflict with the minimum requirements [of the statute].[23]

This may be important to how the courts will respond to Monsanto’s legal challenge to OEHHA’s proposed glyphosate listing. Monsanto’s argument that Proposition 65 improperly delegates lawmaking power to IARC assumes that OEHHA plays no independent role in identifying chemicals known to the state to cause cancer using the Labor Code listing mechanism. OEHHA could counter that that it does play an independent role, since under SIRC v. OEHHA, it has an independent obligation to find that there is evidence sufficient to establish that a chemical is “known to the state of California” to cause cancer.

Under this argument, the Labor Code listing mechanism simply provides OEHHA with authority to use IARC assessments of carcinogenicity as a basis for making that finding. OEHHA’s recently adopted final rule clarifies the circumstances under which the agency can properly exercise that authority, and it provides procedural mechanisms to allow for the introduction of new or different information in a manner otherwise consistent with the law. So long as OEHHA complies with those procedures, it would argue, there is no improper delegation of authority and no violation of any due process or other constitutional requirements.


Monsanto’s constitutional objections to the Labor Code listing mechanism in its lawsuit are novel ones — no similar objections were raised in SIRC v. OEHHA, for example. It remains to be seen whether the procedural safeguards embodied in OEHHA’s regulation will help OEHHA to address Monsanto’s objections. If the courts determine that the procedural safeguards are insufficient, it won’t just be Roundup™ that escapes California’s consumer warning requirements for chemicals known to the state to cause cancer and reproductive toxicity.

For more information, please contact Kevin Haroff in Marten Law’s San Francisco office.

[1] Glyphosate, or N-(phosphonomethyl)glycine, was one of four chemicals proposed for listing in September. The other three are tetrachlorvinphos (an insecticide used to kill fleas and ticks); parathion (an insecticide used in certain agricultural applications); and malathion (another insecticide used in both agricultural and residential settings). See California Environmental Protection Agency, Office of Environmental Health Hazard Assessment Notice Of Intent To List Chemicals By The Labor Code Mechanism: Tetrachlorvinphos, Parathion, Malathion, Glyphosate (September 4, 2015), http://oehha.ca.gov/prop65/CRNR_notices/admin_listing/intent_to_list/pdf_zip/090415NOIL_LCSet27.pdf.

[2] Cal. Health & Safety Code § 25249.5 et seq.

[3] See Petition For Writ Of Mandate And Complaint For Preliminary And Permanent Injunctive And Declaratory Relief, Monsanto v. Office Of Environmental Health Hazard Assessment, et al., Case No. 16CECG001883 (filed January 21, 2016), http://www.monsanto.com/files/documents/monvoehha.pdf.

[4] Cal. Health & Safety Code § 25249.5.

[5] Cal. Health & Safety Code § 25249.6.

[6] Cal. Health & Safety Code § 25249.8(a).

[7] The specific references are to Cal. Labor Code sections 6382(b)(1) and 6382(d).

[8] In addition to listing chemicals as known carcinogens under the Labor Code listing mechanism, OEHHA can list chemicals identified by agencies it determines are “authoritative bodies” for cancer assessment purposes. See Cal. Health & Safety Code § 25249.8(b). IARC has been specifically identified as an “authoritative body” for Proposition 65 purposes, along with the National Institute for Occupational Safety and Health, the National Toxicology Program, the U.S. Environmental Protection Agency, and the U.S. Food and Drug Administration. See 27 Cal. Code of Regulations (“CCR”) § 25306(m).

[9] WHO IARC, IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Preamble 22–23 (2006), http://monographs.iarc.fr/ENG/Preamble/CurrentPreamble.pdf. In addition to Group 1, 2A, and 2B chemicals, the IARC classification scheme includes chemicals that are not classifiable as to their carcinogenicity to humans (Group 3) and chemicals that probably are not carcinogenic to humans (Group 4).

[10] (2012) 210 Cal.App.4th 1082. OEHHA’s overall strategy of listing both known human and known animal carcinogens under the Labor Code listing mechanism was validated by the California Court of Appeal (3rd District) in AFL-CIO v. Deukmejian (1989) 212 Cal.App.3d 425.

[11] See also Sierra Club v. Schwarzenegger (Brown), No. RG07-356881 (Cal. Super. Ct., Alameda, Apr. 24, 2009) (“OEHHA has a mandatory duty to list any chemical for which IARC has concluded there is ‘sufficient’ evidence of cancer in humans or animals. This includes those agents added to the IARC list, whether or not the final monograph has been published.”).

[12] Press Release, “IARC Monographs Volume 112: Evaluation of Five Organophosphate Insecticides and Herbicides” (March 20, 2015), http://www.iarc.fr/en/media-centre/iarcnews/pdf/MonographVolume112.pdf.

[13] IARC Monographs – 112 (Glyphosate), http://monographs.iarc.fr/ENG/Monographs/vol112/mono112-09.pdf.

[14] See “Notice of Intent to List Chemicals by the Labor Code Mechanism: Tetrachlorvinphos, Parathion, Malathion, Glyphosate [09/04/15],” http://oehha.ca.gov/prop65/CRNR_notices/admin_listing/intent_to_list/090415LCset27.html.

[15] (2011) 196 Cal.App.4th 233.

[16] See “Initial Statement Of Reasons, Title 27, California Code Of Regulations, Proposed Section 25904 Listings By Reference to the California Labor Code, Safe Drinking Water And Toxic Enforcement Act Of 1986 (Proposition 65)” (undated), http://oehha.ca.gov/prop65/law/pdf_zip/ISORlabor_code012714.pdf.

[17] See “Notice of Proposed Rulemaking Title 27, California Code of Regulations, Proposed Section 25904 Listings By Reference to the California Labor Code” (Jan. 27, 2014), http://oehha.ca.gov/prop65/law/NPR012714.html.

[18] 27 CCR § 25904; OEHHA, “New Section 25904 Listings by Reference to the California Labor Code” (July 21, 2015), http://oehha.ca.gov/prop65/CRNR_notices/072115NewSec25904.html.

[19] 27 CCR § 25904(b). IARC’s Group 2B classification (“possibly carcinogenic to humans”) applies both to substances for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals; and to substances for which there is inadequate evidence of carcinogenicity in humans but sufficient evidence of carcinogenicity in experimental animals. WHO IARC, supra note 9, at 23.

[20] 27 CCR § 25904(c).

[21] Id.

[22] Id.

[23] 210 Cal.App.4th 1101.


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