Environmental Science and Technology
September 7, 2005


Scientists question the continued use of POEA in Roundup, citing data
showing harmful effects to frogs.

By Rebecca Renner

Glyphosate herbicides, such as Monsanto's popular Roundup, have an
environmentally friendly reputation because their active ingredients
are relatively nontoxic and degrade rapidly in the environment. But
University of Pittsburgh biologist Rick Relyea is challenging this
view. He has found that Roundup at environmentally relevant
concentrations kills or harms tadpoles because of the presence of the
surfactant POEA , an ingredient that is defined as inert and doesn't
appear on the label (Ecol. Appl. 2005, 15, 618-627; 1118-1124).

Relyea's work is one of several studies that shed light on the
behavior of "inerts" in the environment, a topic largely ignored by
the U.S. EPA, say many environmental toxicologists inside and outside
the agency. In 1995, EPA changed the listing of POEA (polyethoxylated
tallow amine) from an inert of "unknown toxicity" to one that is of
"minimal concern". According to the agency, "the current use pattern
in pesticide products will not adversely affect public health or the
environment". The agency presently does not have plans to further
revise the classification, say EPA officials interviewed for this

"The inerts evaluation for environmental effects is EPA's dirty little
secret," says one agency scientist who requested anonymity. "POEA is
likely to be the tip of the iceberg, but we don't know because we
don't have data. The agency assures us that everything's okay. On the
basis of what? Not data. Then, to make matters worse, the inerts
aren't even listed on the label."

An agency official who asked not to be quoted admitted that the
environmental effects of inerts are not a high priority for EPA. This
is not because the agency is ignoring important data, the official
says. Instead, EPA regulators say that any problems are not
significant or are handled through usage restrictions that appear
prominently on product labels.

EPA's approach generally makes sense, argues environmental
toxicologist Keith Solomon with the University of Guelph (Canada). EPA
assumes that pesticide active ingredients are typically potent
chemicals and most inerts are fairly benign, which Solomon says is
generally true. Glyphosate, with its very low toxicity, violates this
assumption. As a result, the inert surfactant makes a big difference
to the overall toxicity of any formulation with the compound. However,
this case is probably unusual, he states.

For regulatory purposes, pesticide formulations consist of two broad
components -- "active" ingredients that target the pest or weed and
"inerts" or "other" ingredients. Inerts, which often comprise the bulk
of the pesticide formulation, improve the efficacy or handling
characteristics of the product, for example, by helping the active
ingredient dissolve, easing application, or improving the pesticide's
adherence to plant leaves. POEA in Roundup enables the herbicide to
penetrate the waxy surfaces of plants, according to Monsanto
scientific director Eric Sachs.

EPA has four lists of inert ingredients: inerts of toxicological
concern, potentially toxic inerts, inerts of unknown toxicity, and
minimal-risk inerts. An indication of the hazards that many inert
ingredients may pose is the extent to which these same chemicals are
regulated under other U.S. laws, says Caroline Cox, staff scientist
with the advocacy group Northwest Coalition for Alternatives to
Pesticides in Eugene, Ore. In March, she scrutinized the more than
1800 chemicals on EPA's list of inerts of unknown toxicity and found
that 75 are identified as hazardous by the Clean Air Act, 52 under
Superfund, 64 in the Clean Water Act, 43 on the Toxics Release
Inventory, and 78 with the Toxic Substances Control Act. In addition,
292 inerts of unknown toxicity are registered by EPA as active
ingredients in other pesticides.

EPA requires information on possible toxicity for active ingredients
but not for inerts.

Moreover, most inert ingredients are not identified on labels because
manufacturers maintain that these constitute trade secrets. The
legality of this position is still being considered by the courts,
according to Cox, whose organization has spearheaded the call for
disclosure of inerts on pesticide labels.

One chemical that appears on the inerts list but is also considered an
active ingredient is PBO (piperonyl butoxide), which is a synergist
that makes pyrethroid pesticides 10x more lethal to black flies and
mosquitoes. Studies of commercial pyrethroid formulations by Eric
Paul's group at New York state's Rome Field Station show that PBO also
enhances the toxicity of these pesticides to fish. However, EPA's
recent PBO risk assessment fails to look at the synergist in
conjunction with the active ingredient. EPA's risk assessment misses
the point, says Paul. "An environmental evaluation needs to know how
these things work together. We know there is a synergistic effect on
target species. This alone suggests the need to evaluate effects of a
formulation on nontarget species," he says.

In the case of POEA, Monsanto disputes the concentrations and
conditions Relyea used in his experiments. However, at least four
other papers dating back to 1988 point the finger of blame at POEA
(Lancet 1988, 1, 299; Arch. Environ. Contam. Toxicol. 1999, 36,
193-199; Environ. Pollut. 2001, 114, 195-205; Chemosphere 2003, 52,
1189-1197.) A fifth, more recent paper reports that tadpoles exposed
in the lab to POEA concentrations common in the environment (0.6
milligrams per liter [mg/L] and 1.8 mg/L) for 42 days, which is the
estimated aquatic half-life of the surfactant, exhibited delayed
metamorphosis and developmental abnormalities (Environ. Toxicol. Chem.
2004, 23, 1928-1938)

Steve Bradbury, director of EPA's Office of Pesticide Programs
Environmental Fate and Effects Division, acknowledges that some
inerts, including POEA, may have toxicological profiles that cause
concern. However, usage restrictions for products containing POEA
clearly state on the label that it should not be applied directly to

Label restrictions miss the point, say Relyea and others, who note
that chemicals in the environment often stray from their intended
locations. For example, when U.S. and Canadian foresters spray
glyphosate herbicides from helicopters and planes onto forest to
eliminate plants after clear cutting, mist inevitably drifts off
target. Frogs living and breeding in wetlands and small ponds in or
near forests are unintentionally exposed to formulations containing
POEA, these scientists note. A study of aerial applications of Roundup
found that small wetlands can receive up to 1.9 mg of acid equivalents
per liter (Environ. Toxicol. Chem. 2004, 23, 843-849).

Several environmental risk assessments conducted for glyphosate
herbicides did not include information from Relyea's work and more
recent studies (J. Toxicol. Environ. Health, Part B 2003, 6, 289-324;
Glyphosate: Human Health and Ecological Risk Assessment Final Report,
SERA TR 02-43-09-04a, U.S. Department of Agriculture Forest Service,
2003). These assessments acknowledge the more potent aquatic toxicity
of POEA and the lack of monitoring, sublethal effects, and
environmental occurrence data. However, they conclude that the risk of
adverse effects in the aquatic environment is generally small.

Nevertheless, an Australian governmental review in 1996 found that the
POEA in Roundup presented a toxic risk to tadpoles and frogs in
shallow water, where dilution doesn't occur. "The use of the POEA
surfactant is an anachronism in light of its well-documented toxicity
and the availability of substitute surfactants with demonstrated lower
toxicities," argues biologist Reinier Mann, who at the time worked in
Australia and is now at the Universidade de Aveiro (Portugal).

"We know [POEA is] toxic," states Canadian Wildlife Service
toxicologist Bruce Pauli, who is the corresponding author of the 42-
day exposure study. "We hope there's not enough in the water to cause
a problem." But at a time when amphibian populations are declining
dramatically for unknown reasons, he asks: "Is that really protecting
the environment?"