POISONS AND TOXINS
Although the terms poison and toxin are somewhat interchangeable, I went to the dictionary to get a clarification of my suspicion that there is a difference. It brought me back to the years when I would occasionally teach a class entitled "Water Pollution Biology". There is an overlap in their meanings but a toxin is more specifically a toxic (or poisonous) organic substance produced by an organism or generated during its decomposition. In general, the poisonous or toxic effect begins at low concentrations. Toxins are generally destroyed by heat but there are often variations in the toxins produced by different strains of bacteria that contaminate food. A few have heat stable toxins that can survive boiling, so spoiled food is not made safe by sterilization.
BIOLOGICAL MAGNIFICATION
The term is often applied to the increase of the body concentration of an aquatic pollutant at each step in the food chain. Major concerns about this increase has often focused on mercury and some organic pesticides that are accumulated by predators and may have an approximately ten-fold increase with each level of the food chain. Thus the concentration in algae may be x (number per unit of biomass). The algae feeders may become 10 x, small fish may be 100 x, large fish 1,000 x, and fish eaters 10,000 x.
The increase can occur if the substance can neither be excreted nor metabolized effectively. Thus mercury, especially a form converted into a organic compound, can be accumulated by its affinity for protein in the body. DDT and many other halogenated (especially chlorine and bromine versions of biphenols) organic compounds accumulate in body fats because of their high solubility in fats and oils, but very low solubility in water. The halogenated biphenyl like structure can be very similar to hormones in some part of the structure and thus even very low concentrations can wreck havoc with normal metabolism.
A similar concern surfaced when hearings regarding the building of a large nuclear power plant was proposed for along the shore of Lake Michigan. Zero emissions in the cooling water to be discharged into the lake was sought because some algae were able to concentrate certain radioactive metals to 30,000 times their concentration in the water. Other processes might concentrate the release still more and make the beach hazardous for sunbathers. The plant was built without allowing such emissions.
LEAD
Lead poisoning may have been part of the problems leading to the decline of the Roman Empire. It is still a serious problem in the United States because of the past use of lead paint, lead anti-knock compounds in gasoline, and lead use in plumbing. The first two have been phased out, but residual effects may still occur in older homes and perhaps roadside soils. Use in plumbing and elsewhere has been eliminated or reduced, except for many service lines from water mains to older residences. Municipal waterlines are usually protected by additives to the water that coats the line and minimizes lead in the water.
Hunters no longer routinely use lead shot or bullets when hunting for food items. Lead glass has generally been eliminated in making decorative wine decanters and glassware. When I was in high school I worked as a "printer's devil" in a newspaper print-shop; much of the type and other materials I handled was made of lead. Can I blame all of my deficiencies today on that?
ASBESTOS
The mesothelioma caused by asbestos exposure can make one frightened of the many uses asbestos was put to in the past. Naturally occurring release of asbestos has probably always been part of out environment. The fibrous crystals can break and release very fine fiber fragments that get into cells and perhaps act by disturbing the normal structure or function of chromosomes. All of us probably have many such crystals in our bodies, but those with extremely high exposure and long term exposure are at great risk, a risk made much higher for smokers.
During my first year of college, I worked a four-hour shift five evenings a week in a furniture factory. About two weeks were spent building a drying facility on the finishing line and lining it with sheet rock asbestos. The sheets were fitted by cutting to needed size with a power hand saw. The heavy asbestos dust soon activated my asthma that had been absent for several years following childhood desensitizing shots. No respiratory or filter masks had been used. Mesothelioma is more apt to be caused by a different one of the four main types of asbestos, especially if the fibers are small, fine, and airborne.
VARIABLE SENSITIVITY TO POLLUTANTS
Variable response to exposure, when graphed, often shows the same bell-shaped curve shown by many biological phenomena. Poisons and toxins are often characterized (LD50 or LC50) by the lethal dose (ingested - LD) or exposure to lethal concentrations (LC) in the water (aquatic organisms) or air (for air breathers) that kills 50% of those tested. The range from no damage to 100% killed can be quite variable. The threshold for a no concern exposure concentration is typically set many times beneath the value at which no affect is first observed. If it cannot be metabolized or eliminated by excretion a greater margin of safety is used.
Most of us realize that too much or too little of a good thing, nutrient or otherwise, must temper our use of a substance. Iodine and sugar are two substances of which too much can kill us, and too little may also be fatal. Ethyl alcohol is not needed but is OK in small amounts, but lethal in large amounts.
CRUDE OIL
Crude oils from different locations are often unique combinations of varying concentrations of a mix of volatile and non-volatile hydrocarbon compounds. Some of the more volatile and toxic components dissipate into the atmosphere leaving longer chain waxes and oils of lower toxicity, but still dangerous to organisms by various physical effects such as clogging feathers, gills, or coating food items. There is thought to be more crude oil released into the ocean from natural underwater leaks than from human caused events. But the natural leaks are diffuse enough to allow oxidation and other processes of decontamination to occur naturally. The massive leaks we are responsible for swamp the natural processes and cause a lot of damage. Ultra-violet light can assist breakdown of volatile organic substances entering the atmosphere if quantities are not extreme.
WHAT'S A PERSON TO DO?
1. Eat a balanced diet. Use sanitary processes in preparation. Organically produced food is fine, but wash fruits and vegetables before using. Use vegetable oils when appropriate. Leafy green vegetables, colorful fruits and vegetables, nuts, and whole grain products are generally good if quantities are reasonable.
2. Take folic acid if you are pregnant, but check with your physician, it can help prevent fetal deformities induced by some pesticides. If you don't eat seafood or live near the ocean, use iodized salt in moderation.
3. Go light on servings of sweets and fatty meat, moderate on eggs, butter and whole milk.
4. Scratch the above, and get some good-eating ideas from a vegan.
AND ANOTHER THING OR TWO
Pesticides in pork do not have as great a biological magnification effect because pigs eat and grow fat quickly and use less food to produce a pound of meat than do some other animals. But bacon and other cured meats with added nitrates or nitrites can produce carcinogenic nitrosamines when browned at high heat; perhaps vitamin C or colorful fruits and vegetables reduce the danger. The biblical prohibition of pork was a wise thing in days before the knowledge of how trichinosis and the trichina worm killed people.
Alcohol, fats, and oils all have about twice the calories per gram as compared to sugar and carbohydrates. They do not provide fiber, but some may have a laxative effect. Fiber is a better way to go with fruits, vegetables and whole grains being good sources. Sorry, I didn't intentionally include a pun in the last statement.
EVOLUTIONARY ADJUSTMENTS TO POLLUTANTS
A classical example of evolutionary adjustments was the industrial melanism exhibited by some moths in England during the industrial revolution. Museum collections show increasing percentages of a dark (melanistic) phase attributed to their not becoming prey of birds when tree trunks became darker from smokestack emissions. When trees became lighter after emissions were controlled the percentages of the dark phase decreased to near the original percentage. Some researchers have questioned the accuracy of the phenomenon.
There are multiple possible ways evolutionary adjustments are made to survive toxins. Sometimes metabolic processes can evolve protection by breaking down the substance, converting it to a non-toxic substance, or provide alternatives to a previously essential process. Behavioral changes can minimize exposure. A study of fly resistance to a pesticide in Scandinavia included use of bristles on the fly to ward off body contact with the pesticide. So life goes on.
Joseph G. Engemann Kalamazoo, Michigan March 7, 2016
No comments:
Post a Comment