The Foodie Farmer: Nutrients Are Pesticides: The Dose Makes The Poison

Most people find it odd that I am a Registered Dietitian who is licensed as a commercial pesticide applicator. I actually find it quite advantageous because what I studied in my nutrition degrees both undergrad and grad school, applies across multiple biological systems, not just human systems, but soil and plant systems too. Because I have a solid understanding of the science of nutrition, I therefore have a solid understanding of the science of pesticides. Many of the nutrients I studied as an RD, have applications as pesticides.

Paracelsus was correct when he coined the term "The dose makes the poison".

First, lets start with some definitions:

Nutrient: "Chemical substances obtained from food and used in the body to provide energy, structural materials, and regulating agents to support growth, maintenance and repair of teh body's tissues. Nutrients may also reduce the risk of some diseases" Whitney & Rolfe, Understanding Nutrition, 9th edition (yes I know, my copy is dated. This is the one I used to tutor undergrads during grad school, not my copy as an undergrad!)

Pesticide: A pesticide is a chemical used to prevent, destroy, or repel pests. (EPA)

Any chemical can be toxic, whether its natural or synthetic, depending on how much you eat, drink or absorb. Nutrients are the chemicals make up of food.

Nutrients in high doses work as pesticides to control bacteria, fungi, molds and mildews, mainly in fruit and vegetable crops. Nutrients are typically used as protectant fungicides, meaning they are used proactively before disease appears to protect the foliage of the plant. Remember from high school biology how important photosynthesis is in the growth and development of a plant? Without foliage, or if foliage is damaged from mildews, a plant cannot photosynthesize efficiently. Photosynthesis is the process that converts sunlight into energy (carbohydrates). Photosynthesis is required for fruits and vegetables to ripen. Without sufficient foliage on the plant, grapes wouldn't ripen and turn sweet, tomatoes wouldn't turn red, watermelon wouldn't get sweet and pink, strawberries wouldn't turn red and sweet. Fungicides, in the form of nutrients like sulfur, copper, zinc, and manganese protect the plant in advance of any disease. They are not "treatments" and do not work after a plant has developed a disease, they only work to protect the plant from developing the disease.

First, let's look at the recommended dietary intake of nutrients for humans:

Nutrient	RDA	UL	Major functions:
Zinc	8-11 mg/d	40 mg/d	Cellular metabolism Protein synthesis Wound healing Cell division DNA synthesis
Manganese	1.8-2.3 mg/d	11 mg/d	Activates many enzymes that are critical to metabolism, bone development, and wound healing.
Copper	700-900 µg/d	5000-10000 µg/d	Critical in the function of enzymes that control energy production, connective tissue formation, and iron metabolism.
Sulfur	No RDA-Metabolic breakdown of the recommended intake for protein and sulfur amino acids should provide adequate inorganic sulfate for synthesis of required sulfur-containing compounds.	No UL	The body does not use sulfur as a nutrient by itself. Contributes to protein structure. Acts as a bridge between amino acids in hormones like insulin.

Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%-98%) healthy people.

Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.

Next, let's look at the recommended application rates of these nutrients as pesticides as approved by EPA:

Pesticide	Rate/Acre	Oral LD50	Controls For:(grapes/tomatoes)
Zinc	3-4 lb/acre	1400 mg/kg	Phomopsis, Black Rot, Botrytis, Downy Mildew
Manganese	1-4 lb/acre	5000 mg/kg	Anthracnose, Early Blight, Late blight, Bunch rot, Downy mildew
Copper	0.75 – 1.75 lb/acre	1847 mg/kg	Downy Mildew, bacterial spot, anthracnose,
Sulfur	3-20 lb/acre	2000 mg/kg	Powdery Mildew, spotted mite, red spider mite.

For comparison purposes - Vitamin D is highly toxic with an LD50 of 10 mg/kg, whereas table salt (sodium chloride) has an LD50 of 3000 mg/kg.

What is LD50?

Oral LD50: An LD50 is a standard measurement of acute toxicity that is stated in milligrams (mg) of pesticide per kilogram (kg) of body weight. An LD50 represents the individual dose required to kill 50 percent of a population of test animals (e.g., rats, fish, mice, cockroaches). Because LD50 values are standard measurements, it is possible to compare relative toxicities among pesticides. The lower the LD50 dose, the more toxic the pesticide.

A pesticide with an LD50 value of 10 mg/kg is 10 times more toxic than a pesticide with an LD50 of 100 mg/kg.

We went from milligrams per day as a recommended dietary allowance to pounds per acre to control for disease. The vastly escalated dose converted these nutrients from dietary healthfulness into effective pesticides.

You can see, although these pesticides are "natural", as in nutrients, they are still toxic. By definition, a pesticide must kill or control something.

There is no such thing as a nontoxic pesticide.

Here is a good graphic that depicts the toxicity of natural versus synthetic pesticides: