If the supply of chemical fertilizers is adapted to the adsorption capacity of the soil (the soil reacts as an ion exchanger) there is no danger of pollution. However if the supply of these fertilizers exceeds the capacity of the soil it may contaminate the ground water and possibly the surface water (rivers lakes) with all the adverse effect we know.

Depending on the amount of fertilizer consumed, it may cause disturbances of the kidneys, lungs and liver and even cause cancer.

This is due to the toxic metals that fertilizers have. Fertilizers remove the nutrients of the soil, damaging the soil and the local environment.

Drinking nitrate and nitrite contaminated water causes a disorder in children known as ‘methemoglobinemia’. This leads to various other disorders such as damage to the respiratory and vascular system, blue coloration of the skin and even cancer.

Toxic limit of fertilizer consumption/absorption may affect kidneys, lungs as well as reported to cause cancer. It also polluted drinking water, increased air pollution, acidification of the soil and mineral depletion of the soil.The major effect was when the toxic chemicals found in fertilizers can be absorbed into the plants and enter the food chain via vegetables and cereals. However, the largest health risk is when the chemicals flow into ground water, which is then extracted for drinking. 

I agree with all the answers provided thus far and would like to add that the ill effects of chemical/synthetic fertilizers use in agriculture are primarily environmental. These become non point source pollution if they exceed the adsorption capacity of the soil. Their sedimentation due to soil loss and infiltration into aquifers contaminate water sources. Fertilizers containing nitrogen and phosphorus are particularly noxious to animal and human health, causing eutrophication and mass death of fish and other aerobic organisms living in water. Methemoglobinimia also known as baby blue syndrome (here in the USA) is caused by excessive nitrogen in drinking water. It affects infants primarily as it accumulates faster in their small bodies that become cyanotic (bluish in color). Eventually an accumulation of nitrogen (-NO3) is metabolized into nitrosamines and these are carcinogenic. Crops respond beautifully to these macronutrients however their use must be complemented by irrigation. Crops may become more attractive to pests and parasites when these are fertilized, making necessary an application of pesticides to protect them. Finally, residues of these chemicals affect the biological diversity of soil organisms, hampering their natural metabolism, which in part regenerates soil fertility.

The hazardous fertilizer chemicals enter our food-chain and increase its concentration at each successive trophic levels causing considerable harm. The chemical produce oversized fruits and vegetables but are prone to insect pest and diseases. When the nitrate of fertilizers is taken up by the human, this nitrate is converted to nitrites by the some microorganisms of our intestine and these nitrites form methaemoglobin after combining with haemoglobin of blood and thus interferes with its oxygen carrying capacity. This disease is called methaemoglobinaemia. There is 0.8% of methaemoglobin in a healthy person but its higher percentage causes various problems and at 80% death occurs.

How Fertilizers Affect our Health 

Fertilizers are a mixture of toxic chemicals which are absorbed into the plants, leading toxins to enter the food chain via vegetables and cereals and water creating health affects increase and spread rapidly -         Contaminated water may contain high levels of nitrates and nitrites, causing hemoglobin disorders. -         Heavy metals such as Mercury, Lead, Cadmium and Uranium have been found in fertilizers, which can cause disturbances in the kidneys, lungs and liver and cause cancer . Over 29 popular fertilizers tested positive for 22 toxic heavy metals, including Silver, Nickel, Selenium, Thallium and Vanadium, all directly linked to human health hazards. -        Ammonium Nitrate exposure cause other health problems such as eye and skin irritation, producing a burning sensation. Inhalation exposure can result in irritation of the nose, throat, and lungs. One can also experience nausea, vomiting, flushing of the face and neck, headache, nervousness, uncontrolled muscle movements, faintness and collapse. -         Potassium Chloride interferes with nerve impulses, and interrupts with virtually all bodily functions and mainly affects heart functioning. It can cause all kinds of gastric and stomach pains, dizziness, bloody diarrhea, convulsions, headaches, mental impairments, redness or itching of the skin or eyes. -         Cadmium : Ultimately enters the human tissues resulting in diseases such as tracheo-bronchitis, pneumonitis, pulmonary edema, renal failure, osteoporosis, and many others. Lettuce (Latuca sativa L.), found in great quantities in countries like Brazil and others in South America, uptake Cd very easily, with an average amount of 870mg Cd/Kg. Yet, human beings, via the gastrointestinal system, only uptake about 5% of the Cd through food. However, those lacking iron can uptake up to 6% more. Hence, this can be harmful to them because Cadmium poisoning, which comes from its excessive intake, can lead to kidney, bone and pulmonary damage. The “Itai-Itai” (it hurts-it hurts, in Japanese) , discovered in Japan in the year of 1912, is caused by Cadmium poisoning, which results in acute pain in the joints and spine

Chemical fertilizers are harmful if excessive quantities are used. This results in contamination of surface water via runoffs and its consequent effects. High levels of nitrates and nitrites in chemical fertilizer may cause hemoglobin disorders. Similarly, researchers reported a substantial role of nitrosamine exposure in Alzheimer's disease and diabetes mellitus. This occur due to a chemical reaction between nitrites from fertilizer and secondary amines or proteins which results in DNA damage, oxidative stress, lipid peroxidation, and pro-inflammatory cytokine activation, which together leads to increased cellular degeneration and death.

Traces of toxic heavy metals are also found in chemical fertilizer. Heavy metals such as Cadmium and Lead have been found in fertilizers, which can cause disturbances in the kidneys, lungs and liver and cause cancer.

Refer to the links below for more details on the health effects of fertilizer in humans;

https://amosinstitute.com/blog/the-health-impacts-of-chemical-fertilizers/

https://eponline.com/articles/2017/12/07/the-hidden-dangers-of-chemical-fertilizers.aspx

Chemical as well as organic fertilisers may become harmful for human health and particularly for the environment only if over-applied - without considering the soil nutrient content and the nutrient removal by the expected yield. As to organic fertilisers, animal manures as key organic fertilisers may be contaminated with hormones and antibiotics. They may also be a source of transmission of human pathogens to fresh food. It is improper to discuss only health risks of chemical fertilisers and ignoring organic fertilisers.

The biggest human health effects reported for chemical fertilizers have been the blue baby syndrome caused by high concentrations of nitrate. Some susceptible individuals might be in risk due to high concentrations of potassium (kidney dysfunction or other diseases, such as heart disease,

coronary artery disease, hypertension, diabetes, adrenal insufficiency,

pre-existing hyperkalaemia)

Respecting all the beautiful responses , let me congratulate the editor of question for tossing up such a beautiful question. Chemical fertilizers have minimum effects on human health compared to insecticides, herbicides and pesticides considering their decomposition products in soil , thereby , jeopardising the rhizosphere biology to damage the crop ecosystem to near reparable limit. Yes , they do have toxic effects on ground water through their leaching , if not applied as per soil test-crop response based module.

We need to bring the concept of Nutrient Holiday for crops based on soil test interpretaion . Even in a non-chemical based concept of feeding nutrients to crops , we do need starter dose of chemical fertilizers to activate the microbial population of soil to sustain their activity at maximum best...

Anything use of higher doses it's harmful for human health if use blanace dose urea concert into protein and amino acids

Chemical fertilizer are important for plant growth but it consider harmful for human,animals .soil ,water when exceed the level allowed and excessive amounts are used specially without measuring soil nutrients quantities

Let me toss up another overlapping question . How many of you think, herbicides, fungicides and insecticides by the virtue of their greater residence time in soil ( degrade so slow ) are more harmful than chemical fertilizers ..? And , which input has greater capacity to enter into human food chain while comparing with chemical fertilizers.?.

The excessive use of chemical fertilizers degrades the ecosystem and then affects public health.

Use of excessive quantity of synthetic fertilizers are harmful for human health. It is contaminating the surface water via runoffs and its consequent effects. High levels of nitrates and nitrites in chemical fertilizer may cause some disease like hemoglobin disorders, Alzheimer's disease and diabetes mellitus.

As chemical fertilizers are composed chemical substances so they have lots of detrimental effects on human health as well as environment.

1. The dust of chemical fertilizers pollute air during application in the field and creates problem while taking breath, skin and eye irritation etc.

2. Water becomes polluted through the runoff of chemical fertilizers, and ultimately we become sick by drinking of this polluted water.

3. Excessive use of chemical fertilizers may toxic to the soil, plant , water and microbes in soil.

Chemical fertilizers hurt the human body and the environment at large. Fertilizer is an environmental pollutant when wrongfully applied, they contribute majorly to environmental toxicity and as a result, find their way to the food chain. Let's take, for instance, aquatic life. Organisms found within are prone to be affected if the washing of this chemical fertilizer is been washed down into the water body. This will lead to eutrophication. When this happens, the water body gets polluted, which will cause respiratory disorders like hypoxia. The drinking water we take, the food we eat, the crops, most of these are products of fertilizer. I hope this helps.

The chemical fertilizers are those fertilizers which supply only one primary plant nutrient, either N or P or K. On this basis, the fertilizers can be straight nitrogenous, straight Phosphatic or straight Potash fertilizers. Use of excessive quantity of synthetic fertilizers is harmful for human health. It is contaminating the surface water via runoffs and its consequent effects. For example, Urea provides only N while Potassium Chloride provides only K.

· Examples of straight nitrogenous fertilizers include Ammonium Sulphate (AS), Calcium Ammonium Nitrate (CAN), Ammonium Chloride and Urea.

· Examples of straight Phosphatic fertilizers include Single Super Phosphate (SSP) and Triple Super Phosphate (TSP)

· Example of straight Potash fertilizer is Potassium Chloride

· Complex fertilizers on the other hand provide two or three primary nutrients in which nutrients of at least two are in chemical combination. For example, Diammonium Phosphate provides both N and P. Further, Mixed fertilizers are physical mixtures of the straight fertilizers. We note here that complex and mixed fertilizers are considered ergonomically better.

Some straight fertilizers have strong acidic nature or Basicity nature when we applied to plant them also harmful for human skin or for eye. They cause skin irritation and ultimately death to tissue.

For more information on effect of straight fertilizers on human and environment please follow this link:https://ohsonline.com/articles/2017/12/07/the-hidden-dangers-of-chemical-fertilizers.aspx

Dear F. Bouteldjaoui . This comes from a chemical reaction between nitrites and secondary amines or proteins and causes DNA damage, oxidative stress, lipid peroxidation, and pro-inflammatory cytokine activation, which together leads to increased cellular degeneration and death.

See kindly the useful link: https://amosinstitute.com/blog/the-health-impacts-of-chemical-fertilizers/#:~:text=The%20Human%20Impact%20of%20Chemical%20Fertilizers&text=This%20exposure%20comes%20from%20a,degeneration%20and%20death%20(14).

Kindly see also the following useful RG link: Conference Paper Investigation of Effect of Chemical Fertilizers on Environment

Also check please the following useful RG link: Article Fertilizer-Derived Uranium and its Threat to Human Health

The following link is also very useful: https://www.sundayobserver.lk/2021/07/04/news-features/effects-chemical-fertiliser-human-health-and-environment