Biogeochemical Cycles: Impact of Fertilizers

Environmental Chemical Pollution

• Anthropogenic substances (man-made chemicals) production has increased dramatically, exceeding 500 million tons per year, contrasting with 5 million tons fifty years ago.
• Over 100,000 synthetic chemicals are present in everyday products, including solvents, detergents, dyes, hormones, antibiotics, surfactants, pesticides, and mineral oil products.
• Global annual petroleum-based liquid fuel production reaches approximately 3 billion tonnes annually, with some quantity released as accidents or leaks and the rest being converted to combustion byproducts.
• Over 300 man-made chemicals have been detected in human blood samples from around the world.

Impact of Chemicals

• Air Pollution and Climate: Ozone depletion, photochemical smog, acid rain, greenhouse gases, and global warming and dimming are consequences of chemical pollutants.
• Land and Water Pollution: Polymers and plastic pollution, toxic metals (e.g., Hg, Pb, Cd, Cr, Zn, Cu, Ni, Co, Se), and organic anthropogenic chemicals (e.g., BTEX compounds, pesticides) contribute to pollution of land and water.

Key Terms

• Persistent pollutant: Resistant to environmental degradation through chemical, biological, or photolytic processes.
• Bioaccumulation: Occurs when an organism absorbs a toxic substance at a rate greater than the rate at which the substance is lost.
• Biomagnification: The increasing concentration of persistent pollutants as they move up a food chain.
• Global Distillation: Persistent organic pollutants (POPs) are transported from warmer to colder regions of the Earth (e.g., poles and mountain tops).

Natural Elemental Cycles

• Biogeochemical cycles (e.g., Carbon, Phosphorus, Nitrogen, Sulphur) describe the path atoms take between living (biotic) and non-living (abiotic) components of the Earth.
• Human activities are significantly altering these cycles, particularly with nitrogen and phosphorus from fertilizers becoming reactive forms that are emitted into the atmosphere, rather than being absorbed by crops.

Examples of Impacts

• Phosphorus cycle: Anthropogenic contributions from phosphate fertilizers disrupt the phosphorus cycle.
• Nitrogen cycle: Human activities convert more atmospheric nitrogen into reactive forms than all terrestrial processes combined, leading to pollution of waterways.
• Fertilizer drawbacks: Fertilizers increase the growth of harmful insects, decrease plant root strength, leading to nitrate accumulation in plants, which can cause the formation of nitrosamines when the plants are consumed.
• Plastic Pollution: Plastic production has grown from 5 million tonnes in 1950 to over 300 million tonnes today. Significant amounts of plastic waste accumulate in the environment and ocean. Plastics are persistent and can accumulate in various environments impacting organisms.

Toxic Metal Pollution

• Heavy metals (Hg, Pb, Cd, Cr, Zn, Cu, Ni, Co, Se) are persistent, accumulate in organisms, and biomagnify. Some exhibit strong endocrine properties.
• Arsenic, lead, cadmium, and mercury are among the top ten chemicals causing public health concerns.

Lead Pollution

• Lead is a bioaccumulative pollutant, potentially interfering with enzyme function, and causing acute and chronic toxicity, including issues related to the developing brain.
• Historic releases (e.g., lead in gasoline) still impact human populations today.
• Exposure to lead can have long-term impacts, with possible links to Alzheimer's disease.

Mercury Pollution

• Mercury is released naturally and by human activities (e.g., coal burning, gold mining). MeHg is highly toxic.
• Biomethylation processes in aquatic environments convert inorganic mercury into methylmercury (MeHg), which bioaccumulates in food chains.

Other Pollutants

• BTEX compounds: Benzene, toluene, ethylbenzene, and xylene. Carcinogenic constituents found in petroleum products and used in various manufacturing processes.

• Pesticides: Organochlorines (e.g., DDT), organophosphates (e.g., chlorpyrifos), carbamates (e.g., carbaryl), and neonicotinoids (e.g., imidacloprid) - often persistent and bioaccumulative, causing various environmental and health concerns and some are banned.

• Dioxins/PCDDs/PCDFs: Products formed during incomplete combustion of organic matter. Multiple toxic effects with diverse impacts on human biological systems.

• Phthalates: Widely used as plasticizers in various products, including toys and cosmetics. Known endocrine disruptors with potential multiple cancer risks.

• PCBs: Polychlorinated biphenyls. Widely used in various applications, but now banned owing to their extreme persistence and bioaccumulation.

• Brominated Flame Retardants (BFRs): Persistent and bioaccumulative, used as flame retardants in plastics and other materials causing numerous neurobehavioral problems and cancers.

Medical Chemicals

• Female hormone estrogen derivatives and compounds, such as 17ß-estradiol, can cause multiple deformations in fish and frogs, including feminization of male fishes and frogs.
• Parabens are commonly found as preservatives in personal care products and can cause endocrine disrupting issues.

Other Ubiquitous Anthropogenic Chemicals

• Polyfluorinated organic substances (e.g., PFOS) are exceptionally persistent and accumulate in organisms causing multiple impacts.
• Methyl-tert-butyl ether (MTBE) is another ubiquitous pollutant with adverse effects on the nervous system.
• Alkyl phenols and bisphenol-A (BPA) are found as endocrine disruptors in various products.