USDA's Pesticide Data Program

Each year, USDA's Pesticide Data Program publishes data on pesticide residues, principally in fruit and vegetable crops, selected in part because of their frequent consumption by children.  It is difficult to know how worried consumers should be about the results.  Here are some thoughts and questions on the most recent 2008 residue detections for fruits and vegetables.

For some pesticides, EPA sets safety tolerances for the maximum amount of residue that should show up on food.  For other pesticides, EPA sets no tolerance, meaning that there should not be any residue of that pesticide at all.

First, we look at data on total residue detections.  Many fruit and vegetable samples have multiple pesticide residues, but the amounts may be small, usually far within the Environmental Protection Agency's safety tolerances.  Let's say for the moment that we are not very worried about these total detections, but instead want to know about detections that violate EPA standards.

		All samples		Residue detections
		#		#		per 100 samples
Asparagus		372		39		10.5
Blueberries		726		1736		239.1
Broccoli		554		797		143.9
Celery		741		3821		515.7
Green Beans		741		1392		187.9
Green Onions		186		272		146.2
Greens, Collard		240		540		225.0
Greens, Kale		318		622		195.6
Nectarines		672		1603		238.5
Peaches		616		2155		349.8
Potatoes		744		1410		189.5
Spinach		747		1850		247.7
Strawberries		741		3703		499.7
Summer Squash		554		1050		189.5
Sweet Corn, Fresh		152		1		0.7
Sweet Potatoes		184		92		50.0
Tomatoes		740		903		122.0
Total		9028		21986		243.5

Second, therefore, we look at residue detections that exceed EPA's established tolerances, for pesticide uses that have a tolerance.  These detections are more worrisome when they happen, but they do not happen very frequently.  Fewer than 1% of samples had this type of residue detection exceeding an established tolerance.

		All samples		Residue detections exceeding an established tolerance
		#		#		per 100 samples
Asparagus		372		0		0.0
Blueberries		726		3		0.4
Broccoli		554		0		0.0
Celery		741		2		0.3
Green Beans		741		2		0.3
Green Onions		186		0		0.0
Greens, Collard		240		11		4.6
Greens, Kale		318		10		3.1
Nectarines		672		0		0.0
Peaches		616		0		0.0
Potatoes		744		7		0.9
Spinach		747		16		2.1
Strawberries		741		2		0.3
Summer Squash		554		5		0.9
Sweet Corn, Fresh		152		1		0.7
Sweet Potatoes		184		0		0.0
Tomatoes		740		1		0.1
Total		9028		60		0.7

Third, we look at residue detections for pesticides that have no EPA tolerance.  The lack of a tolerance may mean that the chemical is judged to be of greater safety concern.  The USDA found many such residue detections -- almost 5 such residue detections per 100 samples, which seems like a lot of detections in violation of EPA standards.  However, the tests are quite sensitive, and the residue amounts may be very small.  USDA is not greatly worried: "In most cases, these residues were detected at very low levels and some residues may have resulted from spray drift or crop rotations."

		All samples		Residue detections for pesticides with no tolerance
		#		#		per 100 samples
Asparagus		372		1		0.3
Blueberries		726		21		2.9
Broccoli		554		17		3.1
Celery		741		123		16.6
Green Beans		741		23		3.1
Green Onions		186		9		4.8
Greens, Collard		240		34		14.2
Greens, Kale		318		45		14.2
Nectarines		672		2		0.3
Peaches		616		61		9.9
Potatoes		744		45		6.0
Spinach		747		33		4.4
Strawberries		741		5		0.7
Summer Squash		554		15		2.7
Sweet Corn, Fresh		152		1		0.7
Sweet Potatoes		184		1		0.5
Tomatoes		740		1		0.1
Total		9028		437		4.8

Environmental groups are not convinced. The Environmental Working Group uses these data as one of several sources in constructing its "dirty dozen" and "clean fifteen" lists of fruits and vegetables.

I wish the USDA's PDP reports did a better job helping readers to understand the implications of residue detections for pesticides that have no EPA tolerance. If USDA's position is that these are negligible detections, attributable to inconsequential pesticide drift, then it should explicitly set a threshold for these negligible detections. On the face of it, without that type of interpretation, I am reluctant to accept that these detections are all inconsequential. For example, notice that 16% of celery samples and 14% of many leafy greens had this type of violation.  Could those really all be spray drift?  That would seem surprising.  It would help to have a more blunt assessment from USDA experts: "These detections are negligible, but we want these other detections to fall into compliance in the near future."

Also, the Environmental Working Group throws a good heavy punch this week regarding the produce industry's government-funded information campaign to convince people not to worry about pesticides.  Agriculture departments, including the California Department of Food and Agriculture and USDA, should steer clear of anything that smacks of misleading propaganda on this topic.  For example, now that I have had time to study the residue data, I suspect last November's report from the Alliance for Food and Farming is overconfident that these residues are harmless.  A better approach might be to undertake some vigorous enforcement, drive down the frequency of violative residue detections, and then boast about the results. Indeed, if industry leaders took a long-term perspective, I think they would encourage USDA to do so.

Pesticide residues are not my leading food safety concern -- they rank behind foodborne illness on my list of things to worry about -- but I do take them seriously.  Among agricultural economists, I sometimes hear an outright dismissal of concern about pesticide residues as completely silly, but I think scientists who study cancer risks and toxicity take these concerns more seriously.  For example, here are the conclusions of the 2008-2009 report from the President's Cancer Panel, issued by the federal government's National Cancer Institute:

The entire U.S. population is exposed on a daily basis to numerous agricultural chemicals. Many of these chemicals are known or suspected of having either carcinogenic or endocrine-disrupting properties.

The report identified several problems that hinder policies to address environmental chemical contaminants: (a) inadequate funding and staffing, (b) fragmented and overlapping agency authorities, (c) excessive regulatory complexity, (d) weak laws and regulations, and (e) undue industry influence.