I've been seeing a lot of conflicting information online about chemical fertilizers being poisonous and was wondering if there are any trustworthy sources of information to definitely answer this question?
It's important to note that synthetic fertilizers are often salts which are sometimes produced by a chemical reaction, hence the "chemical fertilizer" name. They are no more "chemical" than table salt. Salts are simply ionic compounds. And that simply means two things stuck together by "static cling". Table salt is Na+ and Cl-. The plus and minus stick together and you get table salt.
I can think of no more definitive source of information than the MSDS.
If you went to the big box store and picked up a bag of 10-10-10 general-purpose fertilizer, what you will likely find inside the bag are ammonium nitrate and/or urea, potassium chloride, and ammonium phosphate and/or rock phosphate.
Looking at the MSDS for each, we find toxicity levels of common fertilizer ingredients in rats (mg/kg) compared to table salt: (the bigger the number, the more a rat can eat without dying)
Table Salt 3000
Ammonium Nitrate 2217
Potassium Chloride 2600
Ammonium Phosphate 3000
Rock Phosphate No data available since, apparently, it's a rock and not considered toxic enough to bother with a rating.
If you are a 70kg (150lb) rat, you would have to eat at least 6 oz of table salt or fertilizer to expect to have a 50% likelihood of dying. (ie. If you fed 6 oz of fertilizer to ten 70kg rats, 5 would die, 5 would not).
How about and more complete fertilizer like Miracle-Gro All Purpose Plant Food? The ingredients are:
Ammonium Sulfate 2840
Potassium Phosphate 4640
Potassium Chloride 2600
Urea Phosphate 5840
Boric Acid 2660
Copper Sulfate 472
Iron EDTA 5000
Manganese EDTA 2000
Sodium Molybdate 4000
Zinc Sulfate 1260
It appears copper sulfate is the most toxic, at 472 mg/kg, but luckily Miracle-Gro only contains 0.07% copper, so you would have to consume an extremely large amount of this fertilizer to get a toxic dose of copper sulfate. Likewise with zinc sulfate since the product contains only 0.06% zinc.
This product poses minimal risks to humans or animals so exposure is not a significant concern.
Other fertilizers which haven't been mentioned so far:
Potassium Nitrate 3750
Magnesium Sulfate (Epsom Salts) Oddly, I can't find data on this, but people have been soaking their body parts in solutions of it for a long time.
Calcium Nitrate 3900
Calcium Sulfate (Gypsum) : The probable lethal oral human dose has been estimated to be 500 to 5000 mg/kg
Ferrous Sulfate 1520
Calcium Carbonate (Lime) Main ingredient in calcium supplements in the vitamin aisle and in anti-acid tablets like Tums. 6450
This isn't a complete list of every salt possible for agricultural use, but definitely contains the more popular ones... and if you're savvy enough to desire and purchase those not listed here, it's unlikely you'll ever be reading this anyway.
In conclusion, what is poisonous is relative to the amount. Water can be poisonous in large enough amounts, but from what I've seen so far, there is nothing here that is particularly scary.
One caveat to this may be the contamination with heavy metals such as arsenic, cadmium, barium, lead, etc. It has been alleged that zinc is a waste product of the steel industry and thus could contain "who knows what" in addition to zinc.
Websites such as these exaggerate claims and seek to scare an uneducated public by suggesting copper, iron, selenium, manganese, chromium and many others are "toxic heavy metals" while you can find them in any multi-vitamin. Most of the list are, in fact, plant nutrients.
Also, how many of these are naturally occurring in soils? And what levels are considered toxic? As already stated, Miracle-Gro contains 0.06% zinc, which isn't much, and if the zinc is 1% contaminated, I wouldn't expect the overall Miracle-Gro product to have much at all in percentage terms (0.0006%). Of course, 10-10-10 has no zinc at all.
I'll have to research this more, but it's beyond the scope of this answer. Anything can be contaminated.. from food to medicine, so it wouldn't be exclusive to synthetic fertilizers.
Organic fertilizers are no exception:
George Kuepper, an agriculture specialist with the National Center for Appropriate Technology, observed in a 2003 report that composting manure actually concentrates the fertilizer's metal content, which could lead to greater levels of the contaminants in organic soil.
Recent studies have lent Kuepper's concern tentative support. For example, in 2007, researchers conducted an analysis of wheat grown on various farms in Belgium; based on the results, they estimate that consumers of organically grown wheat take in more than twice as much lead, slightly more cadmium, and nearly equivalent levels of mercury as consumers of wheat grown on conventional farms.
The overriding concern is not if chemical fertilizers are safe but if the use of chemical fertilizers is the best option.
When you sit down for breakfast you might have a cheese omelet with whole wheat toast. You don't scoop out 23g of protein, 28g of carbohydrates and 20g of fat from your nutri-tubs. We need a balanced diet consisting of both macro and micro nutrients as well as other components. Plants are the same way. What we feed the plants we use to feed ourselves should be an important consideration.
Soil is also the same way. A healthy soil is full of microorganisms that help create a healthy environment for plants.
If we provide plants with good, nutrient rich, healthy soil the plants will do well with little need for external inputs of fertilizer, insecticides and fungicides.
When it comes to organic gardening and farming, it's not about finding replacements to chemical fertilizers, it's about taking a wider approach to plant management that includes building a healthy soil ecology. Synthetic fertilizers focus on providing nutrients to plants. While organic fertilizers are still labeled with a guaranteed analysis (N-P-K) like traditional fertilizers, the way they primarily work is by feeding the soil microorganisms which in turn feed the plants.
A lot of organic fertilizers also come from more sustainable sources such as waste products from other industries. Compost is entirely made up of waste material. Corn gluten meal, which is a fertilizer that has some pre-emergant herbicidal qualities, is a waste product of the manufacture of corn syrup and cornstarch. Compare that to ammonium nitrate which is made using the Haber Process which requires natural gas. We should all be aware of the detrimental issues surrounding trying to extract more natural gas by now.
In addition, while in low concentrations synthetic fertilizers may be considered safe, those products can have serious risks in the concentrated forms they are transported and stored in prior to use. See http://www.fss.txstate.edu/ehsrm/safetymanual/agsafe/fertilize.html
This material is very harmful if accidentally spilled or sprayed onto body surfaces. It can cause blindness if it gets into the eyes. Also, high concentrations of ammonia gas in the air are very irritating to the lungs.
If I accidentally spill corn gluten meal on myself, I don't have to go through a hazmat shower.
Taking the organic approach helps nature help our plants so we don't need to use synthetic herbicides, insecticides and fungicides, some of which are known to cause serious health problems in humans. With an organic approach you minimize the need for insecticides and fungicides. Insecticides for example not only kill the insects we don't want, but also the insects we do want. Only 3% of the insects in a garden are considered pests. That's why Integrated Pest Management (IPM) is becoming more popular with commercial growers. It reduces the use of unhealthy chemicals and can reduce costs while producing healthier plants. When soil biology becomes unbalanced and pathogenic microorganisms start infecting plants with disease other methods can be used to control disease including corn meal, milk sprays and bio-fungicides such as bacillus subtilis and trichoderma harzianum.
Are chemical fertilizers safe? That's not really the most important concern. Is managing gardens, lawns, crops organically or synthetically an overall better approach is what most people think about when they decide to switch to organic practices. Is everything labeled organic safe? Do we fully understand how to make the most effective use of organic practices? The answer to both those questions is no. There is still a lot of research going on and practices are evolving as we learn more. That doesn't make it the wrong approach.
As to the Slate article you quote you left out some important qualifiers. It is not as one sided as your quote implies.
No one is saying that organic soil has higher heavy-metal counts than conventional soil as a rule—scientists have not conducted enough research to make such a determination. Still, some evidence indicates that organic soil can, in some cases, be more contaminated.
Similarly, a 2007 study of Greek produce found that organic agriculture does not necessarily reduce the cadmium and lead levels in crops. As it turned out, "certified" organic cereals, leafy greens, pulses, and alcoholic beverages had slightly less heavy-metal contamination than conventional products, but "uncertified" organic products had "far larger concentrations" than conventional ones.
I feel my previous answer covers everything that I wanted to say as far as answering the question in regards to the use of synthetic fertilizers in gardening but the asker has issues with it so I'll try to make it more direct and address some of the concerns.This may be boring to some, I think my previous answer is still more useful in terms of gardening.
This is a subject I have been interested and informally studied for years and have had many discussions about. I sometimes forget that not everyone has the same level of experience so I'll try and be more thorough.
First regarding bias. My background is in engineering and I am a computer programmer. I began researching different ways to care for my lawn and was impressed with how effective organic practices were that I decided to start an organic lawn care blog to share what I was learning and the experiences I had for the benefit of others. Other than that site I don't have any financial ties to the horticultural industry. I do have some affiliate links on my site but people generally don't buy 50lb bags of fertilizer online because shipping can be expensive. If people buy more organic fertilizer based on anything I say it likely won't be through my links and I will receive little or no money for it. I share the info because it's what I believe in based on my research and experiences.
I brought up the comparison of organic fertilizers because the comparison was previously made in an answer by the asker in a way I felt was misleading.
Are chemical fertilizers poisonous to people or animals? I've been seeing a lot of conflicting information online about chemical fertilizers being poisonous and was wondering if there are any trustworthy sources of information to definitely answer this question?
What does it mean to be "poisonous"?
Poisonous: "Relating to or caused by a poison."
Poison: The relevant definition is "A substance taken internally or applied externally that is injurious to health or dangerous to life."
Another way to rephrase the question would then be:
Are chemical fertilizers injurious to health or dangerous to human or animal life if taken internally or applied externally?
This is an overly broad question which would take too long to answer in detail. Bottom line... Some are and some aren't. Some are more toxic than others. Some may or may not have acute or chronic toxicity concerns.
For example if we look at the MSDS for potassium nitrate we see:
Routes of Entry: Inhalation. Ingestion. Toxicity to Animals: Acute oral toxicity (LD50): 1901 mg/kg [Rabbit]. Chronic Effects on Humans: May cause damage to the following organs: blood, kidneys, central nervous system (CNS). Other Toxic Effects on Humans: Hazardous in case of skin contact (irritant), of ingestion, of inhalation (lung irritant). Special Remarks on Toxicity to Animals: Not available. Special Remarks on Chronic Effects on Humans: May cause adverse reproductive effects based on animal test data. May affect genetic material (mutagenic) Special Remarks on other Toxic Effects on Humans: Acute Potential Health Effects: Skin: Causes skin irritation. Eyes: Causes eye irritation Inhalation: Breathing Potassium Nitrate can irritate the nose and throat causing sneezing and coughing. High levels can interfere with the ability of the blood to carry oxygen causing headache, dizziness and a blue color to the skin and lips (methemoglobinemia), and other symtoms of methemoglobinemia (see other symptoms under ingestion). Higher levels can cause trouble breathing, circulatory collapse and even death. Ingestion: Ingestion of large quantities may cause violent gastroenteritis with nausea, vomiting, severe abdominal pain. It may also cause colic and diarrhea. Acute toxicity of nitrate occurs as a result of reduction to nitrite. The nitrite acts in the blood to oxidize hemoglobin to methemoglobin which does not perform as an oxygen carrier to tissues causing Methenoglobinemia. Symptoms may include vertigo, muscular weakness, syncope, irregular pulse, convulsions,p. 5 anoxia, coma, fall in blood pressure, roaring sound in the ears, a persistant throbbing headache, generalized tingling sensation, heart palpitations, visual disturbances caused by increased intraocular tension and intracranial pressure, flushed and perspiring skin, which is later cold and cyanotic. Circulatory collapse and death may occur. Chronic Potential Health Effects: Ingestion and Inhalation: Repeated or prolonged exposure to small amounts may affect the blood, respiration and kidneys and produce anemia, Methenoglobinemia with attendant cyanosis and anoxia, hyperpnea and later dyspnea, and nephritis.
That sure sounds like it would be "injurious to the health of humans and animals" (both acutely and chronically) to me which means it would be poisonous to humans and animals by definition.
Smaller doses are less injurious than larger doses in most cases and some poisons have beneficial uses for humans. See warfarin (a rat poison) and botox (a lethal neurotoxin). That doesn't mean they're not "poisonous".
It's important for users of these products to understand the products and use them as directed to minimize risks. That is why there are laws concerning labeling and use of these products. Many states have begun enacting regulations that require commercial applicators of garden fertilizers and pesticides to receive a license that requires passing a test. The misuse of some of these products (organic products included) can lead to potential health and environmental problems. If someone on the Internet says he mixes these chemicals with their bare arm, that doesn't mean it's a good practice.
In addition to reading the labels consumers who want to be informed should refer to the MSDS and independent research that has been published in peer reviewed journals or distributed by recognized entities such as government agencies for the given products they intend to use.
Some other clarifications I feel are necessary that have been brought up in discussion:
What is an MSDS
MSDS is an acronym for Material Safety Data Sheet. For full information see wikipedia. In summary it is a document required to be provided by manufacturers and/or importers that highlights some important information as it relates to the occupational safety of workers who handle or are otherwise exposed to the product, emergency responders that may have to deal with spills, fires, explosions, contamination and medical personnel that may have to treat patients that have been exposed to these materials.
It is not the be-all and end-all to information about the safety of a material. For that, independent research is very important.
Some MSDS will include the NFPA 704 diamond which is a quick way to analyze the hazards of the substance.
What is LD50
This is the metric Randy used in answering his own question to determine whether the products were poisonous or not. LD50 is short for "lethal dose, 50%" usually referred to as mean lethal dose. This is provided in the MSDS to indicate acute oral toxicity. It can also be labelled in other ways. This is just one example of a component's toxicity and is not the only way to define the toxicity of a substance which is why I feel his answer is fundamentally flawed and dangerous.
In general we don't willingly expose fellow humans to every substance we think might kill us in order to determine the safety so animals are used instead. A given population of an animal is administered doses of the material orally and observed over a set period of time. When the administered dosage is enough to kill 50% of the sample that dose is considered the mean lethal dose.
A proper LD50 indicates what the dose is as a ratio of mass of dose to mass of subject for the given species. You'll see something like 100 mg/k [rabbit]. The lower the LD50 the less toxic it is. The dosage can be administered a number of different ways including orally and intravenously.
Given a smaller dose, you would assume that a smaller percentage of the species would die but the metric used is when 50% of the sample dies. It's not like everything is fine until the mean lethal dose is reached. If you're one of the ones that dies with a smaller dose, well I guess it sucks for you.
The species is specified because LD50 varies by species. If we look at the MSDS for ferrous sulphate it lists a number of different LD50's for it's components administered to different species in different ways:
Ferrous Sulfate Heptahydrate (7782-63-0): LD50 (Oral-Mouse) 1520 mg/kg; LD50 (Intraperitoneal-Mouse) 245 mg/kg; LD50 (Intravenous-Mouse) 51 mg/kg
LD50 can even vary within a species. See this article on chocolate toxicity in dogs.
Unless specific data is available for humans, we can only guess at how it will affect us by looking at how it affects other animals but it does provide some useful information.
Long term exposure
In addition to acute toxicity, compounds can potentially adversely affect health with repeated exposure. "What doesn't kill me only makes me stronger" is not always true. Sometimes things will slowly cause injury that over time develops into serious health problems. These may be listed in the MSDS for a product. When these issues are present it's important to follow recommended guidelines in the use and handling of the product.
This is probably the most important toxicity information to look at concerning fertilizers as we're not normally ingesting them but are exposed to small amounts as they are applied in our environment. The toxicity varies by compound and the question is too broad to cover all synthetic fertilizers individually. There are also issues with some organic fertilizers as well.
Indirect adverse effects on health.
I addressed this in my original answer and in a comment so let me just connect some of the dots.
Some synthetic fertilizers are known to be harmful to microorganisms (see Organic and synthetic fertility amendments influence soil microbial, physical and chemical properties on organic and conventional farms). For example boric acid (which Randy indicated is an ingredient in one common fertilizer) is mutagenic for bacteria and yeast according to the MSDS.
Other fertilizers also have adverse effects to soil biology. Referencing LD50, if the dose we apply to a garden is so small we don't have to worry about it, maybe a little strong for a rat, likely harmful to an ant, how does that dose affect the bacteria which are orders of magnitude less mass than the subjects that are tested? What do they do to insects?
The microbiology of the soil as well as the insects are important for the health of the plants. When good microorganisms die we can be left with pathogenic species or insects that are pests. The chemical approach to dealing with these is to apply synthetic insecticides and fungicides. These are more hazardous chemicals in general. So if the use of some synthetic chemicals necessitates the use of other hazardous chemicals it doesn't necessarily make them poisonous but it does indirectly affect human health adversely.
The health of the plants we consume contributes to our overall health. There have been a number of studies on this. Some of the most notable and earliest were done by William Abrecht who believed there was a link between poor soil and poor human health. He conducted many studies and published many papers on that hypothesis. He also believed that synthetic fertilizers were contributing to creating poor soil.
His contemporaries have also conducted similar research. Some of his work and theories are contested, some have been disproved but the notion of good soil=good produce=healthy people is one of the foundations of organic production. Some of these are not new ideas. Organic production uses a lot of old techniques. They are just being researched and formalized more these days.
I specifically mention Albrecht because Randy has referenced Albrect's work in other parts of the site and thought he would be aware of one of his fundamental views as it pertains to this question.
Wow. Chronic exposure to fertilizer is toxic? You do realize many fertilizers are made up of components used in Medicine? Potassium chloride is used to treat hypokalemia. I am not saying you should start putting spoonfuls of the stuff from a 50lb bag meant for the field, but dosage is the issue. Small doses are necessary for the body to function properly. Large doses are toxic.
Material Safety Data Sheets (MSDS) exist to provide the user/applicator with information on how to properly use the product, what to do in case of an accidental over-exposure and the levels to be concerned about.
ALL organic fertilizers break down into the same components that synthetic fertilizers do, as far as plants are concerned. Too much fertilizer is BAD.
Soil organisms will actually consume Urea when the soil is too wet to stay alive. They break down the fertilizer to get at the oxygen component. For the farmer this is bad as the soil bacteria consumed his plant food. This is called denitrification.
The main concern for ALL fertilizer sources is salt content. Too much salt restricts the ability of roots to take up water efficiently. Whether this salt comes from Fresh Manure, you urinating on the lawn (Urine is high in Urea) or putting on too much fertilizer, the effect is the same.
Check the MSDS on ANY fertilizer bag and you can see all of the heavy metal content. You can NOT do that with many organic fertilizers. Many manure composts are high in heavy metals, have too much phosphate fertilizer, etc. Remember manure runoff and why it is so bad? There is too much phosphate "fertilizer" in that manure. The animal eats large quantities of organic matter, defecates the excess phosphate, farmer puts it on the field, crop can't use it all and the next rain washes the excess into the lake or stream and we have algae blooms.
You need to understand chemistry, even the basics, in order to know how all of these nutrients are used in the soil.
From first hand experience I can tell you YES, it is poisonous and I almost died from SKIN exposure.
It was summer, I had been off work and gardening a lot to fill my spare hours waiting for job offers to come in. Unfortunately I'd also been drinking a lot of beer for a few weeks, perhaps my liver was overtaxed.
I was sweating, and handling synthetic 10-10-10 fertilizer with my bare hands. I thought nothing of it, had done it before with no ill effects noted. However this time, perhaps it was also that the dust got on my arms, or that I didn't rinse it off soon enough.
Either way, about 15 minutes later I barely had any strength, fell to the floor and could not sit up. I asked someone to get me a beverage but the idiot stood there dumbfounded instead of just doing it ASAP - Enough water might have helped but since the person there couldn't walk and chew gum at the same time, let alone pour some water into my mouth, at least I managed to convince them to call 911. My breathing was labored and I felt close to death, and I am not one to feel like that - it was a very new, scary experience that I have thankfully not encountered again.
I was very dizzy and barely conscious for the next few hours, with the hospital just observing me, offering no further treatment than the saline IV I had been given in the ambulence on the way to the hospital.
I drank about 1.5 gallons of water and excreted it fine, trembling and room spinning. It didn't help that I didn't realize at the time that the curtain around my bed was waving a lot from the central air blower so when I thought I saw it moving, it really was moving (lol).
Anyway, I am now extremely cautious about fertilizer contact and know for certain that plain old 10-10-10 is bad news. I do still use it bot won't even put it on my lawn unless it's supposed to rain soon, so that pets won't have excessive contact until it rains in. Granted I have a flat lawn so that runoff isn't an issue.