Agricultural Chemical, or Agrochemical, is a term given in reference to fertilisers and pesticides [1a]; with each having different effects on our environment. My personal opinion is that the environmental problems associated with the use of Fertilisers are most significant, and so intend to evaluate whether these impacts are offset by their yield success.
Fertilisers can be found in two forms, Organic (Carbon-based matter) and Inorganic (Simple Chemicals). Both contain proportions of Macro and Micro nutrients vital for plant growth. Macronutrients necessary for increased crop yield are Nitrogen (N), Potassium (K) and Phosphorous (P) and are found most concentrated within Inorganic Fertilisers. Micronutrients such as Boron, Manganese, Zinc and Iron [2], are only ever required in small quantities; and can be mainly found in Organic Fertilisers.
Farmers use fertilisers to increase crop yield, as they contain nutrients that may have been removed or leached from the soil by preceding crop growth or by weathering. Farmers aim to utilise the correct amount and type of fertiliser for their particular crop; i.e. Cabbage needs good healthy leaves, and so will require large supplies of nitrogen; a nutrient necessary to leaf growth as required for Amino Acid Synthesis [3]. Nitrogen cannot be obtained from the atmosphere, and must be assimilated from the soil as Nitrates. These Nitrates can be added to the soil by the farmer through the use of a Fertiliser. This great technological breakthrough in the early 20th century of blending Nitrates, Phosphates and Potash to create crude Inorganic Fertiliser was vital to the increase in world food supplies due to increased yield [4].
This Cabbage Farmer has chosen to add Inorganic Fertiliser to his crop, as it is here that the desired Macronutrient is the most concentrated. Inorganic Ammonium Nitrate Fertiliser has a Nitrogen composition of 34%, compared to an Organic Fertiliser such as Cattle Manure having only 0.6% [1b].
As anticipated, the crop yield begins to increase, with his cabbages of improved size and quality. However, just beyond the boundary of his land, an environmental disaster is commencing. The stream is overrun by aquatic plants, as vigorous algae growth covers the surface. As he tests the water, he notices that the Oxygen content has fallen dramatically. This is due to a process known as Eutrophication, and is the main impact of fertiliser use. Eutrophication is a natural process, defined simply as the aging of lakes and streams as a cause of nutrient enrichment [5]. Thus, if it is a natural process, then why is it considered a problem? It is human action, and the use of agrochemicals, which have accelerated this problem to such a rate that our environment cannot cope, with serious problems occurring as a result.
Those applied Nitrates not taken up by crop plants, i.e. if an excess has been applied, are leached into the nearby stream by surface run off. These ions, along with others such as Phosphates from the faeces/urine of livestock, cause a vigorous growth of algae and aquatic plants. A rapid decay of algae can then occur, often due to the toxicity of excess ions. Organic Matter is decomposed by bacteria, whose respiration reduces the Oxygen concentration of the water. Oxygen deficiency leads to the mortality of the other members of the community; thus affecting the food webs of the ecosystem as a whole.
The environmental impacts of this are dire, and effect more than just the local plant population. Eutrophication can have deadly effects to humans too. This was evident in the Chesapeake Bay area of the Eastern United States in 1997, as local water sources became infected with Pfiesteria Piscicida a toxic bacteria that can cause serious neurological problems when ingested in substantial amounts, i.e. if it comes into public water supply. This occurred due to the Cyanobacterial bloom that resulted from agricultural run off from across the drainage basin [5].
Another ecological impact of eutrophication is reduced biodiversity. As nutrient enrichment occurs, it is the primary producers of the ecosystem which thrive, causing Oxygen levels to fall. Invertebrates, Fish and Shellfish begin to suffocate as the Oxygen deficiency reaches Hypoxic Level. Beyond this point, conditions can become Anaerobic; allowing such Bacteria as Clostridium botulinum to thrive. These produce toxins which are deadly to all other marine organsims, including mammals and birds. This is then called a Dead Zone. The largest existing Dead Zone is a 5 800 square mile region at the mouth of the River Mississippi[6]; where thousands of litres of nutrient rich run off from America’s main agricultural land meet the sea; affecting an area of important Shrimp Fishing Grounds.[7]
A further impact of Eutrophication is the toxicity that it causes. Rather than the Bacteria grown in the conditions, it is the Algae itself which is toxic. Harmful algaes produce toxic compounds which can be lethal when concentrated further up the food chain. An example of this is when humans consume Shellfish that have ingested the harmful toxins, resulting in Paralytic, Neurotoxic and Diarrhoetic Poisoning.
If these high level of Nitrate Ions remain in the water beyond treatment, they can be fatal to human babies. It has been discovered that bacteria living in the human digestive tract can denitrify these nitrates into nitrites; which react with Haemoglobin to form Methemoglobin a form of the Protein which does not combine with Oxygen. Thus, the baby will suffocate. [8]
In conclusion, we can fully comprehend that the environmental problems associated with using agricultural chemicals are extreme and irreversible; and therefore must consider whether the Cabbage Farmer’s increased crop yield, due to the use of Inorganic Fertiliser, is worthy of the loss of a baby’s life, or of an entire drainage basin of species. My personal opinion, formulated via the study of the sources and information presented above, is that although agricultural chemicals have aided the progress of many famers, crops and economies; the current impacts on our environment are too great to ignore.
Thus, I suggest that as much money as is earned within the Fertiliser Industry i.e. Britain’s largest company, ICI Fertilizers, made a profit of 407m in 2006 [9] be reinvested into the implication and development of such preventative measures as Buffer Zones, Artificial Sedimentation, Livestock Waste Removal Policies, and purpose built waterways, to ensure that the problems experienced today do not extend into tomorrow.
