8 Major Water Borne Diseases Part III

Dr. Sunil Mittal

9.1 Introduction: Chemical contamination of water

Microbial contamination of water is in prime focus among all types of water contamination. But, last few decades, chemical contamination of water also got significant attention due to their probable adverse health impacts. Chemical contamination of surface or groundwater is resultant of natural or anthropogenic activities. A numbers of potentially harmful chemical contaminants have been identified in drinking-water which are usually present in extremely low concentrations. Pesticides, fertilizers, metals/heavy metals, organic compounds and anions are the major chemical contaminants in water. More than 200 chemical constituents have been documented in groundwater alone. Agriculture chemicals, urban runoff/storm water and municipal point sources are the largest pollution sources of surface water and are responsible for groundwater pollution through leeching process. Chemical contaminants are associated with diabetes, hypertension, nervous disorder, cardiovascular problem, cancer etc. and have impacts on every part or system of human being and other living beings. The complete list of chemical contaminants with their sources and health effects are enlisted in Table 3.2, 3.3 and 3.4.

9.2          Major types of chemical contaminants include:

1. Organic contaminants
2.  Inorganic contaminants
3.  Radiological contaminants

9.2.1     Organic contaminants mainly include

1. Agricultural Chemicals
2. Oil and Petrochemicals

9.2.1.1 Agricultural Chemicals

Agriculture chemicals are one of the major sources of chemical contamination in water. Agriculture is both the cause and victim of water pollution. It causes water pollution through discharge of pollutants and sediment to surface/groundwater. Use of wastewater and polluted surface and groundwater, contaminates crops and transmit diseases to consumers and farm workers. The major classes of agricultural chemicals are given in Table 3.1 on the basis of their applications.

• Nitrate, chloride, heavy metals, organic pollutants, etc. released from fertilizers/pesticides enhances the level of contaminants in groundwater due to leaching through soil and poses threats to public health.
• Runoff of fertilizers and pesticides to surface waters causes dysfunction of ecological system by the loss of top predators due to growth inhibition and reproductive failure.

Organochlorines and organophosphates are two major classes of pesticides, which are extremely toxic

• Organochlorine pesticides -. DDT, benzene hexachloride, toxaphene, methoxychlor, aldrin, dieldrin, chlordane, mirex, kepone, and lindane are the major chemicals under organochlorine pesticides. Most of the harmful organochlorine pesticides are already banned by Environmental Protection Agency in most of the countries. But, still, they are harmful due to their persistence nature.
• Organophosphates pesticides – commonly used organophosphates are chlorpyrifos, parathion, methyl parathion, malathion, diazinon, phosmet, dichlorvos, fenitrothion, azamethiphos tetrachlorvinphos and azinphos-methyl.

Pesticides damages endocrine, immune and detoxification systems of the body. Pesticides cannot be completely detoxified by the body and therefore accumulate in the tissues, where they continue to cause dysfunction and disease.

9.2.1.2 Oil and Petrochemicals

• Petrochemicals can be defined as a large group of chemicals derived from petroleum and natural gas and are used for a variety of chemical purposes. The pollution of oil and petrochemical in water cause serious health concern in aquatic and living beings.
• Gasoline, diesel and benzene and others petrochemicals may contaminate the water supply by leakage from underground storage tanks.
• Methyl tertiary butyl ether (MTBE) and benzene are known carcinogen and possess chronic toxicity to human and other living beings.

Petrochemicals give rise to a number of organic contaminants. The chief organic contaminants and their health impacts are mentioned in Table 3.2.

9.2.2     Inorganic contaminants

Metal/heavy metals and anions mainly contribute to inorganic contaminants in water. Heavy metals and anions contamination in water is a serious health concern since few decades due to their probable association with various adverse health impacts like, nervous, lung, kidney, cardiovascular, skeletal diseases, etc. and various types of cancer.

Heavy metals – Arsenic (As), lead (Pb), uranium (U), mercury (Hg), cadmium (Cd) nickel (Ni) and chromium (Cr) Anions like sulfate (SO42-), nitrate (NO3-), chlorides (Cl-) and fluorides (F-)

The complete list of heavy metals and major anions with their health impacts and sources are enlisted in Table 3.2.However, some important chemical like arsenic, cadmium, mercury, nitrate, iodine and fluoride and their health effects are described in detail in further sections.

9.2.2.1 Arsenic

Arsenic is a carcinogen and potential environmental hazard. Arsenic (As) has influenced human history probably more than any other element due to its toxicity. Around 70 countries and 137 million people affected by arsenic pollution. WHO describes arsenic contamination of Bangladesh’s water supply as “the largest poisoning of a population in history”.

Sources: Arsenic is released into the environment and water through both natural and anthropogenic activities. Natural – Weathering of rocks and minerals Anthropogenic – Pesticides, insecticides, fertilizers, fly-ash and mining practices.

Form of Arsenic– Both inorganic and organic forms. Arsenite [As(III)] and arsenate [As(V)] are the common inorganic form and As(III) is more toxic than As(V). Mode of exposure – Mainly through ingestion of contaminated water.

Health impacts of Arsenic

Arsenicosis is a chronic illness which is implicated due to exposure of arsenic contaminated water over a long period (Fig 1a & b). It is very difficult to diagnose early symptoms of arsenicosis. Arsenic also increases the risk of cardiovascular, kidney, lung disease and certain types of cancer (e.g. skin, bladder and lung). Apart from this, both As (III) and As (V) inhibit pyruvate dehydrogenase. As (III) interferes with phosphorylation (citric acid cycle) reaction as a result no ATP is formed.

9.2.2.2 Cadmium

Cadmium is extremely toxic heavy metal and a carcinogenic chemical. Sources – Discharge during the smelting of metals like zinc, lead, copper, etc. and manufacture of nickel-cadmium rechargeable batteries found in mobile phones/cordless equipment. It is also used in metal plating, some paints, plastics and fertilizers.

Mode of exposure – Cigarette smoke, ingestion of cadmium-contaminated foods. Old galvanized and new plastic (PVC) pipes are sources of cadmium in drinking water.

Health Impacts

Cadmium may affect the kidneys, lungs and bones. Itai-itai disease is a resultant of cadmium poisoning (Fig 2). The kidney is the principal organ targeted by chronic exposure to cadmium. “Itai-itai” or ouch-ouch disease was first described in post-menopausal Japanese women exposed to excessive levels of cadmium over their lifetimes in Jinzu River basin in Toyama, Japan.

Symptoms

• Osteoporosis, osteomalacia, softening of bones and severe renal dysfunction are the primary symptoms of this disease.
• Sometimes normochromic anemia and low blood pressure.
• Average urinary cadmium level in these patients is 20-30 ìg/g-creatinine of cadmium in urine

9.2.2.3 Mercury

Mercury is a naturally occurring element found in air, water and soil.

Mercury has three forms: (1) Elemental mercury (2) Inorganic form and (3) Organic form.

Organic form is extremely toxic.

Sources  –  Natural  source  mainly  include  volcanic  activity.  Major  sources  of  mercury pollution are anthropogenic like mining, industrial effluents, batteries, fluorescent light bulbs, thermometers, pesticides and fungicides. Mode of exposure – Most toxic form of mercury is methylmercury, concentrated in the food chain. The primary medium of exposure occurs through ingestion of water and contaminated food.

Health Impacts

• Minamata disease is a result of methyl mercury poisoning in humans by ingestion of fish and shellfish exposed to methyl mercury. Minamata disease is a neurological syndrome caused by severe mercury poisoning. Symptoms include ataxia, numbness in the hands and feet, general muscle weakness, narrowing of the field of vision and damage to hearing and speech.
• Mercury exposure at high levels can harm the brain, heart, kidneys, lungs and immune system.
• Binding  of  mercury  to  cell  membrane  may  cause  the  imbalance  of  membrane. permeability to K+, affecting the neuronal transmission process, mental retardation and chromosomal defects.

9.2.2.4 Nitrate

Nitrate is an inorganic compound that occurs both naturally and synthetically in the environment. Nitrate is one of the most common groundwater contaminants in rural areas. Nitrate in groundwater originates primarily from fertilizers, septic systems and manure storage. Unavailable nitrogen from the fertilizers leaches to the groundwater in the form of nitrate. This can elevate the concentrations of nitrate above permissible levels in groundwater affecting the drinking water quality.

Nitrates cause eutrophication in water environment. Eutrophication makes the adverse condition for aquatic system and creates oxygen deficiency to aquatic organisms. The whole scheme of eutrophication is given in fig 4 & 5.

Health Impacts

Methemoglobinemia – Regulation of nitrate in drinking water is very important because excess  levels  can  cause  methemoglobinemia  or  “blue  baby”  disease  (Fig  6).Blue-baby syndrome usually occurs in rural areas, where the primary source of drinking water are wells. Methemoglobinemia    most    often   affects   infants   of   less    than   six    months   in   age. Methemoglobinemia is the condition in the blood which causes infant cyanosis, or blue-baby syndrome.  Methemoglobin  is  probably  formed  in  the  intestinal  tract  of  an  infant  when bacteria convert the nitrate ion to nitrite ion. One nitrite molecule then reacts with two molecules of hemoglobin to form methemoglobin. This alters the form of blood protein, prevents the blood cells from absorbing oxygen and causes suffocation to the infants which may lead to death. Due to oxygen deficiency, blue and purple tinge appears on the lips of infants. So, it is named as blue baby syndrome.

Nitrate is not classified as a carcinogen, but prolonged exposure to nitrate results endogenous reduction into nitrite by nitrosation reactions and forms highly carcinogenic N-nitroso compounds in the stomach, large intestine, colon as well as bladder. N-nitroso compounds are one of the strongest known carcinogens, act systemically and can cause cancer in digestive part of body.

9.2.2.5 Iodine

Iodine is a non-metallic trace element that is required by humans for the synthesis of thyroid hormone. Thyroid hormone is secreted by thyroid gland. Thyroid gland is a small butterfly-shaped gland in the neck. Thyroid hormone is required throughout the life for normal growth, neurological development and metabolism. The impairment of iodine level causes goiter and hypothyroidism like disorder.

Goitre

Iodine deficiency results adverse health disorders such as thyroid gland enlargement (goiter) and severe physical and mental retardation (cretinism).Goiter is swelling of the thyroid gland that causes lump formation in the front of the neck.

Symptoms:

• coughing
• a tight feeling in throat
• changes voice, such as hoarseness
• difficulty in swallowing
• difficulty in breathing.

Insufficient iodine intake impairs the production of thyroid hormones, leading to a condition called hypothyroidism.

• Hypothyroidism has adverse effects in all stages of development but is most damaging to the developing brain.
• Maternal iodine deficiency during pregnancy can result in maternal and fetal hypothyroidism, as well as miscarriage, preterm birth and neurological impairments in offspring.

The recommended dietary allowance (RDA) for iodine intake is 150 micrograms (μg)/day in adults, 220 μg/day in pregnant women and 290 μg/day in breast-feeding women.

9.2.2.6 Fluoride

Fluoride is the anion of fluorine. Fluoride is essential for strong and healthy teeth. But, amounts more than acceptable limits produce toxicity to the human being. Water borne fluoride is another leading cause of morbidity in many parts of the world, including the Indian sub-continent, Africa and the Far East, where concentrations of fluoride can exceed 10 mg/l. In India, around 60 million people are affected by excessive fluoride.

Sources– Granite rocks and anthropogenic sources like household products.

• The major household products containing fluoride are following:
• Toothpaste (eg., sodium monofluorophosphate) Dietary supplements (eg., Sodium fluoride)
• Glass-etching or chrome-cleaning agents (eg., ammonium bifluoride)
• Insecticides and rodenticides (eg., Sodium fluoroacetate).

Health Impacts

• Long-term exposure to fluoride through elevated levels in drinking water leads to skeletal and dental fluorosis.
• Fluoride’s suppressive effect on the thyroid is more severe when iodine is deficient.
• Fluoride-induced nephrotoxicity is kidney injury due to toxic levels of serum fluoride.
• Fluoride also effects endocrine system. But its mechanisms remain unclear.

The other heavy metals and anions are enlisted in Table 3.3 with their health impacts and permissible limits in drinking water set by World Health Organization.

9.2.3      Radiological contaminants

Radiological contaminants are chemical elements with an unbalanced number of protons and neutrons that results in emission of ionizing radiation. Examples of radiological contaminants include cesium, plutonium and uranium.

Radiological contaminants emit radiation, which cause damage to DNA and can lead to mutations and cancer. Plutonium, a radioisotope remains radioactive for a long time if it accumulates within the body and continues to damages for many years unless it is excreted.

Preventive Measure

The most effective way of reducing contaminants in drinking water is by

1. 1. Controlling sources of contamination
2. Applied and fruitful research is necessary to remediate and detoxify contaminants.
3. Educate public and society to reduce source contamination and options for treatment.
4. Preventative measures such as modification of tilling methods and run-off control in agriculture.

Use of lined catchment ponds for treatment of wastes and double lined underground storage tanks can significantly reduce contamination of drinking water sources.