Case Study: 2,4-D   World health organisation & us epa

World Health Organisation

June 2015: The herbicide 2,4-D was classified as possibly carcinogenic to humans (Group 2B), based on inadequate evidence in humans and limited evidence in experimental animals. There is strong evidence that 2,4-D induces oxidative stress, a mechanism that can operate in humans, and moderate evidence that 2,4-D causes immunosuppression, based on in vivo and in vitro studies. However, epidemiological studies did not find strong or consistent increases in risk of NHL or other cancers in relation to 2,4-D exposure.

To date, studies providing evidence that 2,4-D can be used as a pesticide on our food are limited. They are usually unpublished and unavailable for peer review. They are directly supplied by the pesticide corporations that sell the chemical. The studies often show concerning results that are frequently dismissed.

The study that sets the international ADI ( Reference Dose ) for 2,4-D is a 1993 private dog study of 5 female and 5 male beagle dogs.

The World Health Organisation 1996 evaluation reveals studies establishing a NOAEL, a no observable effect level as low as 1mg/kg per bodyweight per day. As a result the 1971 ADI of 31mg/kg was changed in 1993 to a 1mg/kg ADI/RfD.

'An ADI of 0-0.01 mg/kg bw was established on the basis of the NOAEL of 1 mg/kg bw per day in the one-year study of toxicity in dogs and the two-year study in rats and using a safety factor of 100.' 1996 JMPR 

There are much lower level studies that are never accepted by the WHO, US EPA and European Commission.

Independent public interest researchers study pesticides at lower levels than corporate researchers who follow 'industry standards'. However public studies are not requested or considered as part of  these critical studies.

The carcinogenicity studies held by the EPA to identify 2,4-D as 'non-carcinogenic' are only supplied by Dow corporation or the 2,4-D pesticide industry taskforce.

The companies that sell the product supply the studies that establish a 'no-carcinogenicity' rating.

FAO Evaluations - 2,4-D use on food in pre-harvest application:

2,4-D is used world-wide for the pre- or post-emergence or pre-harvest treatment of winter and summer cereals.

2,4-D is used as a plant growth regulator pre-harvest on grapefruit and oranges, and post-harvest on lemons. Foliar spraying of grapefruit and oranges with 2,4-D is a minor use.

Industry and independent studies indicated 2,4-D is dangerous at very low levels years before 2,4-D use was extended to include application on our wheat, durum, rye and 2,4-D resistant GM foods. 2,4-D is sprayed on wheat, durum, rye as a harvest aid before harvest.  

Residue levels of 2,4-D on cereals was raised to 2 mg/kg in 2001.

Is the margin between allowable residue levels and industry research too slim for public health purposes?

2,4-D used in Genetically Modified crops

Corn DAS-40278-9 - with increased tolerance to 2,4-D
Soybean DAS-68416-4 - tolerant to 2,4-D and glufosinate
Soybeans DAS-44406-6 - tolerant to glufosinate, 2,4-D and glyphosate tolerance

The genetic modification providing resistance to 2,4-D is insertion of a bacterial aryloxyalkanoate dioxygenase gene, aad1. 

Most recent 1996 WHO Evaluations - toxicity studies:

Short term toxicity:

Since renal lesions occured in a dose-related manner including at the lowest dose tested (5 mg/kg bw/day) there was no NOAEL (Serota 1983a)

The NOAEL was 1 mg/kg bw per day based on renal lesions characterised as cellular alterations in the proximal convoluted tubules in three of three males and one of four females. (Schultze 1990a)

The NOAEL was 1 mg/kg bw/day on the basis of renal toxicity. (Serota 1983b)

Long term toxicity and carcinogenicity studies:

The NOAEL was 1 mg/kg bw/day on the basis of the increase in kidney weights and renal lesions. (Serota 1987)

The NOAEL was 1mg/kg bw per day on the basis of the histopathological lesions seen in the kidneys of animals of each sex. (Serota 1986)

The NOAEL was ...5mg/kg per day in females on the basis of decreases in body weights, body-weight gain and food consumption, increases in liver enzymes, decrease in thyroxine concentration, increases in absolute and relative thyroid weights, and histopathological lesions. (Jeffries et al., 1995)

The NOAEL was 1mg/kg per day on the basis of alterations in serum chemical parameters and histopathological lesions in liver and kidneys.  (Dalgard 1993d. Dow.)

The  2,4-D studies that establish the world health organisation ADI/RfD for 2,4-D:

Dalgard, DW. “52-Week Dietary Toxicity Study with 2,4 D in Dogs. Hazleton Washington, Inc. Report No. HWA 2184-124. 12/2/93. MRID No. 43049001. HED Document No. 011271.

In a chronic toxicity study, beagle dogs (5/sex/dose) were fed diets containing 2,4-D (96.5t) at 0, l, 5, or 7.5 m/kg/day for . 52 weeks. No treatment-related effects were seen on survival, clinical signs, ophthalmology, hematology, urinalysis, organ weights or gross pathology at any dose level. Body weight gains of dogs at 1 mg/kg/day were comparable to those of the controls. Body weight gains were decreased in both sexes at 5 and 7.5 mg/kg/day, with the effect being more pronounced in females at the high dose. The increases in BLTN, creatinine, total cholesterol and ALT activity in dogs at 5 and 7.5 mg/kg/day were corroborated with histopathological changes in the liver and kidneys of these dogs. The increases in BUN and creatinine are compatible with either dehydration or mild 26 Carcinogenicity Peer Review of 2,4-D (4th) July 17, 1996 renal tubular epithelial compromise while the elevations in ALT activity are indicative of hepatocellular injury. The increases in total cholesterol are nonspecific but are typically seen with alterations in lipid metabolism by the liver. Histopathology revealed: a minimal increase in the frequency and average severity of sinusoidal lining cells of the liver of females only at 5 and 7.5 mg/kg/day; minimal increases in the frequency as well as average severity of perivascular, chronic active inflammation of the liver; and an increase in pigment in the tubular epithelium of the kidneys in both sexes at 5 and 7.5 mg/kg/day. The NOEL was 1 mg/kg/day and based on alterations in clinical chemistry parameters (HUN, creatinine, total cholesterol) and histopnthology (liver and kidneys), the LOEL was 5 mg/kg/day. 

Serota,D.G. 1986: Combined Chronic Toxicity and Oncongenicity Study in rats with 2,4-D Acid. Unpublished report No. 2184-103 from Hazleton Laboratories America, Inc. Vienna VA, USA, Submitted by WHO Industry Task Force II on 2,4-D Research Data, Indianapolis, Indiana, USA.

(Query: The 4th US EPA Carcinogenicity Peer Review lists: Serota, DC. "Combined chronic toxicity and oncoqenicity study in rats with 2,4-D acid". Hazleton Laboratories America, Inc. Report No. 2184-102, 5/29/86, ACCESSION. No. 263112-263114. RED Document No. 004498. Reference numbers differ.)

Grounc of 50 male. and 50 female Fischer 344 rats were fed diets containing technical-grade 2,4-D (purity, 97.5%) at doses of 0, 1,5, 15, or 45 mg/kg bw per day for two years.

 Groups of 50 male and 50 female Fischer 344 rats were fed diets containing technical-grade 2,4-D (purity, 97.5%) at doses of 0, 1, 5,   15, or 45 mg/kg bw per day for two years. Haematological, clinicalchemical, and urinary parameters were evaluated before treatment and after 2, 52, and 78 weeks of treatment. Necropsies were conducted on 10 rats of each sex at each dose after 52 weeks and on all surviving  animals after two years. No treatment-related effects were seen on  survival, clinical signs, or gross pathological appearance. Body weight gain was significantly (p < 0.05) decreased in females at 45 mg/kg bw per day at 12 months (-7%) and at 24 months (-9%); noadverse effects were seen in females at the lower doses or in males at any dose. Food consumption was decreased (-2.4%) in females at45 mg/kg bw per day. No treatment-related effects were seen on haematological parameters. Clinical chemistry revealed a significant (p < 0.05) increase in alanine transaminase activity in males (50%) and females (43%) and a decrease in thyroxine level in females (-18%) at 45 mg/kg bw per day at termination. No treatment-related effects were seen on urinary parameters. Males at 45 mg/kg bw per day had significant (p < 0.05) increases in the absolute (9%) and relative (13%) weights of the kidneys after 52 weeks, while females at this dose had significant increases in absolute (10%) and relative (16%) kidney weights after 104 weeks. Thyroid weights were significantlyincreased at termination in males (absolute, 22%; relative, 26%) and females (absolute, 24%; relative, 26%) at 15 mg/kg bw per day and in males (absolute, 26%; relative, 29%) at 45 mg/kg bw per day; females at 45 mg/kg bw per day also showed increases in absolute (2%) and relative (16%) thyroid weights, but the increases were not statistically significant. Histopathological examination revealed renal lesions in males and females at 5, 15, and 45 mg/kg bw per day, including an increased frequency of a brown tubular epithelial-cellpigment, pelvic microcalculi, and transitional epithelial-cell hyperplasia secondary to microcalculi. Brown tubular-cell pigment was seen in 2/50 (4%), 1/50 (2%), 9/50 (18%) 18/50 (36%), and 19/59 (38%) males and 8/50 (16%), 10/50 (20%), 23/50 (46%), 20/50 (40%), and 15/50 (30%) females at 0, 1, 5, 15, and 45 mg/kg bw per day, respectively.The increases reached statistical significance (p < 0.05) at doses > 5 mg/kg bw per day. Increased incidences of pelvic microcalculi were seen in 2/50 (4%), 2/50 (4%), 4/50 (8%), 8/50 (16%), and 11/50 (22%) males and in 19/50 (38%), 11/50 (22%), 15/50 (30%), 23/50 (46%), and 35/50 (70%) females at 0, 1, 5, 15, and 45 mg/kg bw per day respectively. A slight increase in transitional epithelial cell hyperplasia was seen in females at 45 mg/kg bw per day (11/50; 22%) in comparison with controls (0%).

No treatment-related neoplastic lesions were seen at any dose. There was an increase in the incidence of brain astrocytomas in male rats, with 1/50 (2%), 0/50, 0/50, 2/48 (4%), and 6/50 (12%) seen in  the controls and in rats at 1, 5, 15, and 45 mg/kg bw per day,  respectively. Although there was a positive trend (p = 0.002), a pairwise test did not show statistical significance (p = 0.055) when the incidence at the high dose (6/60) was compared with that of the  controls (1/50). The brain astrocytomas are not attributable to treatment because they did not occur earlier in treated rats than in  controls (no decreased latency); there were no preneoplastic lesions such as gliosis in treated rats, and all the tumours were solitary;  the tumours in the treated rats were no larger or more anaplastic than generally seen in control rats (the largest and most lethal tumour was seen in a control rat); and the tumours were seen only in animals of one sex. In another study in Fischer 344 rats (Jeffris  et al., 1995;  discussed below), no brain tumours or any evidence of carcinogenicity was seen in the same strain of rats treated at more than three times  the dose (175 mg/kg bw per day) that was tested in this study. The
NOAEL was 1 mg/kg bw per day on the basis of the histopathological lesions seen in the kidneys of animals of each sex (Serota, 1986).


US EPA 2005 Reregistration Eligibility Decision for 2,4-D (RED)

The US EPA gives a Chronic RfD = 0.005 mg/kg/day. 

Based on  Rat Chronic Toxicity Study: Jeffries, T.; Yano, B.; Ormand, J. et al. (1995) 2,4-Dichlorophenoxyacetic Acid: Chronic Toxicity/Oncogenicity Study in Fischer 344 Rats: Final Report: Lab Project Number: K/002372/064. Unpublished study prepared by The Dow Chemical Co., Health and Environmental Sciences. 2020 p. MRID 43612001

LOAEL = 75 mg/kg/day based on decreased body-weight gain (females) and food consumption (females), alterations in hematology , and clinical chemistry parameters, decreased T4 (both sexes), glucose (females), cholesterol (both sexes), and triglycerides (females). 

There is evidence of neurotoxicity, including clinical signs such as ataxia and decreased motor activity in pregnant rabbits following dosing during gestation days 6-15 in studies on 2,4-D itself and 2,4-D amine salts and esters, and tremors in dogs that died on test following repeat exposure to 2,4-D. Incoordination and slight gait abnormalities (forepaw flexing or knuckling) were also observed following dosing in the acute neurotoxicity study with 2,4-D. There is also evidence of developmental toxicity, as discussed above in the FQPA Special Safety Factor section. In addition, the Agency determined that a repeat 2-generation reproduction study using the new protocol is required to address specific concerns for endocrine disruption (thyroid and immunotoxicity measures).
— 2005 2,4-D US EPA assessment (RED) page 19

The US EPA 2005 assessment also required  (a) Subchronic inhalation toxicity study (28-day) and (b) Repeat two-generation reproduction study (using the most recent Agency protocol) addressing concerns for endocrine disruption (thyroid and immunotoxicity measures).

The US IRIS database does not indicate that these studies were ever supplied. And if they were they were supplied by 2,4-D Industry Task Force, the association that comprises manufacturers of 2,4-D herbicide.

Further reading:

The Charles studies: These respected 2,4-D published studies have strong industry links.

2,4-D : How industry dominates the US EPA carcinogenicity studies that prove ‘not carcinogenic’.

Neurotoxicity: the EPA 2,4-D pesticide study giving the safe level for neurotoxicity – straight from Dow laboratories.

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