Toxic Harvest: The Unseen Costs of Chemical Agriculture

The most productive farm economy in the world has a serious chemical 
addiction. US farmers and ranchers, who control over half of the 
nation’s land, apply 770 million pounds of pesticides each year. By the 
US Environmental Protection Agency’s account, there are 890 active 
ingredients sold in 20,700 different pesticide products registered for 
use in the US. The $11.9 billion that all Americans (not just farmers) 
shell out for pesticides annually represents one-third of the world 
market.
Corn leads the way by far in terms of pesticide use, consuming 225 
million pounds per year. That is more than double the volume used on 
potatoes, the distant second, followed by citrus and soybeans. Cotton, 
though less than four percent of US crop acreage, ranks fifth for 
overall pesticide volume used. Atrazine, the leading pesticide 
ingredient by volume, has been detected in 80 percent of the drinking 
water wells tested. That may come as less of a surprise when you 
consider that 75 million pounds of atrazine are applied each year on 
American soil.
The Tip of the Iceberg
The effects of this activity on wildlife and aquatic life are severe. 
The US Fish and Wildlife Service estimates that 750 million birds are 
exposed to pesticides annually. Of these, at least 72 million birds are 
killed annually by legal pesticide use in the US. Whole populations of 
waterbirds, turtles, and field and range species are in steep decline.
It is likely that a lot more mortality goes unobserved. Most of the 
casualties are probably of small and widely dispersed animals, so that 
even a trained state wildlife biologist searching for carcasses in a 
cornfield would probably find few. A dead sparrow is well camouflaged, 
and it would be only a day or two before a scavenging red fox or 
raccoon carried it off. Studies have shown scavengers remove up to 92% 
of dead birds from a crop field within 24 hours.
There have been well-publicized incidents of pesticide-caused mass
die-offs, and the victims were either large and highly visible, or they 
died in large groups in high visibility places. An estimated 20,000 
Swainson’s Hawks were discovered dead in the Argentine pampas, poisoned 
by the pesticide monocrotophos. Even that great a number might have 
escaped detection were it not for the fact that a few hawks wore radio 
transmitters that led trackers to the scene. Some 10,000 American 
Robins were found poisoned in two Florida potato fields; in another 
instance, a single application of the pesticide fenthion for mosquito 
control killed several thousand migrants of 37 species. According to 
Pierre Mineau, head of the Pesticide Section for Environment Canada’s 
National Wildlife Research Sector, we can only assume that the ones we 
do find are just the tip of the iceberg.
Exposure to modern chemical pesticides and herbicides afflicts animals 
in subtle, non-lethal ways that are not as visible as massive die-offs. 
By targeting the central nervous system, these chemicals reduce wild 
animals’ ability to function and behave normally in the wild. They 
become more vulnerable to predators, disease and exposure. Their 
ability to successfully reproduce and rear young is reduced. While not 
as dramatic, the effect is as fatal as administering a lethal dose of 
poison.
Don’t Cast That Stone
While farmers and ranchers bear an important responsibility for the 
health and welfare of wildlife because of the vast land area they 
control, it is important to resist the impulse to blame only them for 
our chemically-permeated environment. Consumers demanding meat, grains, 
and produce year-round at low prices share the blame. So do homeowners, 
who administer an increasing share of the total amount of pesticides 
applied in the US — not for food, but for gardens and perfect, 
weed-free lawns and fairways. A survey by the US Environmental 
Protection Agency (EPA) estimates that nearly three quarters of US 
households use pesticides in some form. In their book, Redesigning the 
American Lawn, Herbert Bormann and his co-authors estimate that we 
dispense 67 million pounds of pesticides per year in our passionate, 31 
million-acre love affair with grass. Until the public demands otherwise 
and demonstrates a willingness to pay for a substantial change in 
modern agriculture, everyone — rancher, farmer, and homeowner alike — 
must share the burden of responsibility for the proliferation of 
pesticides.
Our Chemical Legacy
Pesticide use became widespread in the 1930s as a means of controlling 
insect and rodent pests in food and fiber crops. They were sprayed from 
the air or from tractors, or cast on the land much like sowing seeds — 
an ironic similarity that brought many an unsuspecting animal, thinking 
it was eating grain, to its demise.
The first generation of chemical pesticides was organochlorines such as 
DDT, whose creator was awarded the Nobel Prize for discovering the 
means of ridding the world of mosquito-born diseases like malaria. 
Organochlorines share the characteristics of being soluble in fats and 
having a long life in the environment. Their persistence is evidenced 
by the fact that traces of DDT in the environment are still detected 
years after it was discontinued because of concern over human 
contamination. But it is the birds that suffer the most because 
organochlorines bind with calcium, and as a result, paper-thin 
eggshells are crushed in the nest by the weight of the parents.
DDT use has been banned in the US. Yet despite its known problems, DDT 
is still being manufactured, and its use continues in other countries. 
A Broad-winged Hawk migrating from North to South America accumulates 
DDT in its body tissue by feeding on contaminated prey species there; 
the effect is to remobilize the chemical in the environment, bringing 
it to places where its use might have long been abandoned. This 
scenario is currently being played out in Africa, India, and other 
parts of the world where DDT is still used.
Second Generation:
  more toxic, less persistent
Once organochlorines were largely phased out in the US, they were 
replaced by a second generation of pesticides called organophosphates 
and carbamates. They are in widespread use today because they do not 
possess the worst characteristics of their organochlorine predecessors: 
they are relatively short-lived and are readily metabolized — they do 
not accumulate in the body. But two other characteristics make these 
chemicals highly dangerous to wildlife: they are extremely toxic, and 
they target the nervous system by binding with cholinesterase enzymes 
that help transmit signals between nerves.
Organophosphates and carbamates are broad-spectrum pesticides, meaning 
they affect a wide range of species. However, their toxicity is more 
acute in birds and reptiles than mammals or amphibians. Partly because 
of their extreme toxicity to birds and reptiles, scientists have tended 
to focus on incidences of lethal poisoning. However, their interference 
with cholinesterase in the nervous system causes a wide range of 
behavioral and physiological symptoms. Depending on the dose, weather 
conditions, and frequency of application, animals might die from acute 
poisoning or exhibit subtle, sub-lethal effects that are very difficult 
to observe and diagnose.
A Revelation Out of “Control”
The sub-lethal impacts of pesticides are so subtle that for years, 
nobody knew how — or even whether — organophosphates and carbamates 
impaired animals’ ability to survive in the wild. In fact the 
connection between pesticides and these subtle shifts was detected 
quite by accident when Manomet’s Kathy Parsons was monitoring 
contaminant effects in polluted urban estuaries, using populations 
feeding in rural Cape Cod wetlands as her control — or “pristine” — 
sample.
“We were surprised when we discovered lesions on chicks in 75% of the 
Black-crowned Night Heron nests that we were monitoring on Cape Cod,” 
Parsons recalls. Dermestid beetles living in bird nests caused the 
lesions. They are a natural and beneficial part of the ecology of a 
nest because they feed on food scraps and guano — nature’s sanitation 
crew. Why were the beetles turning on the chicks? An effect of low 
cholinesterase in young birds is lethargy; if a nestling is not moving 
around, the beetles feed opportunistically on live tissue. “That was 
causing lesions,” says Parsons. “The Snowy Egrets we were using as 
monitors of coastal environments didn’t have the lesions even though 
they were nesting in the same trees and had beetles in their nests.” 
The egrets feed in tidal flats on little flounder and mummichogs; the 
Black-crowned Night Herons Parsons was monitoring on Cape Cod were 
feeding in freshwater wetlands, including cranberry bogs. That was 
Parsons’ first clue in sorting out the complexities of sub-lethal 
pesticide exposure.
At first, Parsons could not explain the drop in cholinesterase levels 
nor why the birds had lesions. But compared to the Snowy Egrets, the 
heron chicks also had low fledge success. It took years of scientific 
sleuthing before it emerged that low cholinesterase was the cause. “We 
were finding pesticide residues in their food and on the feet of adult 
birds. Pulling it all together, we have a complete story that they are 
being poisoned. And it’s sub-lethal — it’s not the kind of poisoning 
that causes them to keel over,” says Parsons.
Once she knew what to look for, Parsons was able to sample 
cholinesterase levels in the blood of turtles and box-nesting birds on 
cranberry farms, orchards, and row crops. In addition to lower fledge 
rates, Parsons observed that birds with low cholinesterase are more 
vulnerable to predators and do not reproduce as successfully. “Manomet 
is about more than trying to develop scientific information, so we 
began monitoring farm habitats directly with box nesting birds to see 
if we could help solve the problem by using that information to develop 
better farm management practices,” says Parsons.
Farmland is Habitat Too
Parsons’ work raises important questions about the way our rural 
agricultural landscape is managed. Since farm and rangeland comprise 
half the private land area in the US, how can pest management integrate 
the broader considerations of fish and wildlife living in these 
habitats? “‘Conventional’ farmers using pesticides far outnumber 
organic farmers,” says Parsons. “If we get them to put up nest boxes 
just to see if we get dead birds in the box or see if they are 
fledging, that would be a huge first step to an awareness that there 
are a lot of other things living in this habitat.”
A decade after her discovery of lesions on heron chicks, Parsons has 
developed easily-replicated methods for tracking and monitoring turtles 
and box-nesting Tree Swallows and Eastern Bluebirds in a variety of 
farm habitats. She has formed partnerships with orchardists, cranberry 
growers, and row crop farmers from Massachusetts to Maryland (see 
Chestertown, p. 18). She has observed cholinesterase values decline 
over the course of a growing season, and suspects that repeated 
exposure to pesticides has a role.
Parsons effectively used spotted turtles as an indicator species for 
understanding pesticide processes on cranberry farms. Cranberries 
require intensive care. To control weeds and pests, farmers sand and 
flood the bogs. They dig ditches and clear upland vegetation to manage 
the surrounding landscape. Conventional cranberry farmers also use a 
lot of herbicides to control weeds. In 1999, the first year of tracking 
spotted turtles for blood cholinesterase levels on cooperating 
cranberry farms, one farmer used a lot of pesticides. But in 2000 when 
the cranberry market sagged and prices fell, the same farmer applied 
fewer chemicals because it was not cost effective. “We know that the 
year when fewer pesticides were applied, cholinesterase levels were 
higher for turtles on the farm than in the [previous] year when more 
pesticides were applied,” says Parsons.
Collateral Damage
Aside from altered neurological function from pesticides, wild animals 
also must contend with the havoc wrought by agricultural chemicals on 
their habitat and food supply. Herbicides drifting into field edges 
physically reduce nesting habitat and the ability of these edges to 
support the rich insect life critical for birds. Animals inhabiting 
farmland unwittingly place themselves most at risk from this chemical 
fallout by eating pesticide treated seeds, scavenging poisoned prey, or 
feeding on agricultural pests such as grasshoppers, grubs, and 
cutworms. The Savannah Sparrow preys on grasshoppers, but if spray 
drift eliminates this food supply, it could starve. Carbamates are 
especially toxic for earthworms, but the violent coiling of a poisoned 
worm would likely be attractive to a hungry robin; this has resulted in 
several documented cases of poisoning with the insecticide carbofuran. 
Though neither the sparrow nor the robin is intentionally targeted, 
both are casualties in the chemical warfare being waged on farmland. 
Yet while these indirect impacts may be severe, they continue to 
afflict wildlife nationwide: US herbicide consumption accounts for 
one-fourth the global total.
The challenge is finding a balance that recognizes the beneficial role 
that farmland birds and insects play in controlling pests. Robert 
Keese, an organic cranberry farmer on Cranberry Hill Farm in Plymouth, 
MA, says herbicides not only control weeds, they harm the beneficial 
insects that prey on pests by eliminating their habitat. Without 
natural predators to control pests, conventional growers are forced 
into a cycle of increasing chemical dependence with every dose. 
“They’re fighting bugs all the time,” says Keese. “Herbicides increase 
your need for insecticides because you’re also eliminating your 
beneficial insects. So they blanket the bogs with pesticides one year, 
and the insects come back the next year stronger than ever.”
Farmer Attitudes
Play a Key Role
The changing attitudes of farmers towards pesticide use will play a key 
role in the future of farmland habitats. Farmers tend to be 
independent, which makes outreach and education a challenge. Denise 
Keehner, head of the Division of Biological and Economic Analysis in 
EPA’s Office of Pesticide Programs, is optimistic and says that now is 
a prime time to work with people who have a stake in the outcome. “The 
coming generation of farmers is more savvy and aware of the 
environmental consequences of their actions than those of 50 years 
ago,” says Keehner. “The majority of them are college educated and 
attuned to pest development cycles. They know how to minimize their 
pesticide costs while maintaining yields. And a lot have a strong 
environmental ethic.”
But the promise of the next generation of farmers might be tempered by 
the risks posed by the next generation of pesticides. While 
organophosphates and carbamates had a fairly cheap diagnostic tool in 
cholinester-ase, the upcoming pesticides lack such a “biomarker.” “This 
new generation has a broad range of new chemistries that aren’t as easy 
to group, so it makes it that much harder to document exposure,” says 
Environment Canada’s Pierre Mineau. “We have a real problem with these 
new chemicals in that sometimes we don’t have a good means of 
diagnosing a kill. We can have a pile of dead birds and not know which 
chemical to test for. We can’t even detect them chemically.”
Mineau contends that when companies place a new chemical on the market 
they should be required to provide a similar biomarker and method to 
validate the chemical’s residue in animal tissue. Newer agricultural 
chemicals are applied at very low application rates — ounces per acre 
compared to 10–100 pounds per acre for the current generation 
pesticides — making detection next to impossible. EPA’s Keehner says 
some newer pesticides target physical mechanisms, such as growth 
regulators, that may be specific to one insect. “It’s an effective way 
of managing that pest because it’s more targeted, so the impact is not 
so broad,” says Keehner. “The down side is that growers will have to 
come up with a menu of pesticides to control other pests.”
The scientific uncertainties of our pesticide dependence are compounded 
by ethical, economic, and moral questions. The majority of people — be 
they farmer or homeowner — buy pesticides to kill pests, not wildlife. 
Yet our appetite for pesticides has hardly dampened, despite their 
lethal impacts. Efforts by scientists like Kathy Parsons to monitor 
pesticide impacts are gaining momentum. Their work is sure to bring 
about increasing public awareness; hopefully it will also bring 
heightened sophistication. With our transition from organochlorines to 
cholinesterase inhibitors, we are learning the hard way that reducing 
toxic exposures of pesticides comes down to the need for substantial 
reduction in chemical proliferation, not swapping one form of toxin for 
another.
— Bob Moore is Managing Editor of Conservation Sciences