1. c. The WQA Glossary of Terms defines heterotrophic plate count or HPC as procedure for estimating the total number of live nonphotosynthetic bacteria in water. Colony forming units (cfu) are counted after spreading an aliquot portion of water sample over a membrane or pour plate and incubating for standard time in an amiable growth medium (agar) and at an amiable temperature.
2. a. Organisms in Earth’s ecosystem may be categorized in three types: Producers, consumers and decomposers. Producers, or autotrophs, are algae, plants and certain bacteria that can produce their own food from simple raw materials. Most use sunlight as an energy source and carry out photosynthesis. They are called auto (self)-trophs (nutrition) because they do not need other organisms for their food and energy.
3. True. Animals, and human beings, are consumers. The consumers, as well as the decomposers, are heterotrophs. Heterotrophic organisms are dependent upon producers for food and energy. They are called hetero (other/different)-trophs (nutrition) because they require the products produced by other organisms, the producers, for their sustenance. Bacteria and fungi are the heterotrophic decomposers. The decomposers are an important component of the ecosystem because they break down the wastes and bodies of dead organisms, making their components available for reuse. Heterotrophic bacteria are the most abundant creatures on Earth. They can be found in great numbers almost everywhere — in air, in liquids, such as milk and water, and in and on the bodies of plants and animals. It has been estimated that despite their small size, the total weight of all bacteria in the world exceeds that of all other organisms combined. Thank heaven, because if these decomposers did not exist in such great numbers, nutrients could not be digested and would remain locked up in complex organic molecules and bodies of plants and animals, and the supply of elements required by living systems would soon be exhausted.
4. d. Many home water treatment units used in remedying a contaminant of concern also include activated carbon for the removal of the disinfectant for aesthetic (taste and odor) reasons, or often to enhance the overall treatment process. This combined with the fact that the operation of these units is inherently intermittent, means HPC levels in water sampled without much flushing can be high. This has been studied and presented by many researchers.
5. False. We are exposed to countless HPC microorganisms throughout our personal environment every day. For example, tens of thousands of such bacteria are permitted and typical in Grade A milk, yogurt, pickles, wine, apple cider, fruits and vegetables, while such foods and many others are still fresh, pleasing and healthful to eat. One may inhale thousands more heterotrophic organisms per breath from normal air. Healthy skin hosts hundreds of thousands per square inch, and in the healthy mouth itself, each milliliter of saliva contains as many as 150 million heterotrophic organisms. Over one million HPC organisms per milliliter have been isolated from chlorinated municipal tap water that has stood quiescent in household water pipes for a period of time.
6. c. While there can be some opportunistic pathogens in HPC colonizations that can affect individuals with compromised immune systems, in general, proliferation of HPC organisms serves to prevent the growth of frank pathogens or opportunistic pathogens. Many people associate the words disease and bacteria to such an extent that they cannot hear one without thinking the other; but, this is a false association. Most bacteria are not harmful. As stated in answer #5, many species of bacteria colonize our skin, digestive tract, upper respiratory tract and other body openings. The number of bacteria that inhabit the lower digestive tract is so great that nearly half the dry weight of feces is bacteria. Bacteria of this normal microbial community (sometimes called the normal flora) generally compete successfully against the pathogenic bacteria that occasionally happen upon the scene. By preventing the multiplication and spread of pathogens, the normal flora helps protect us against possible disease. This same phenomenon occurs in GAC water filters. The U.S. EPA conducted research wherein several POU carbon filters on chlorinated tap water were inoculated with frank pathogens (Salmonella typhimurium), opportunistic pathogens (Pseudomonas aeruginosa, Serratia marcesens, Klebsiella pneumoniae, Yersinia enterocolitica and Aeromonas hydrophila) and several coliforms (Enterobacter aerogenes, Enterobacter cloacae, Citrobacter freundii and E. coli). The findings: None of the enteric or harmful type organisms could compete and survive well with the natural heterotrophic flora growing in the GAC filters; none reached a level considered to be an infective dose even for a health compromised consumer. Two other comprehensive epidemiological studies conducted by the U.S. EPA and Yale University demonstrated that there was no difference in illness levels between control populations drinking chlorinated municipal tap water and test populations drinking POU and POE GAC filtered water with inherently higher HPC concentrations.
7. False. There is no Safe Drinking Water Act maximum contaminant level (MCL), and no maximum contaminant level goal (MCLG) established for heterotrophic plate counts. As part of the U.S. EPA’s Surface Water Treatment Rule, 40 CFR 141.72 allows waterworks to substitute documentation of HPC levels less than 500 cfu/ml for chlorine residual analyses, as evidence that disinfection is adequate.
8. True. It is wise to monitor HPC in public water distribution systems, not because of a direct health relationship, but because they can be an indirect surrogate for detecting other undesirable water main conditions, such as reduced disinfectant residual, excessive biofilm accumulation in slow moving water or a cross connection. This is not the case with a home water filter, however, where we often are intentionally removing the chlorine taste and we know water entering the unit is microbiologically safe.
9. True. Coliform bacteria are found in human and animal intestines and wastes. These aid in digestion of food, and are not pathogenic or disease-producing. Coliform bacteria are the widely used indicator organism to show the presence of sewage wastes in water and the possible presence of associated disease-causing organisms. Escherichia coli (E. coli) is one of the fecal coliform bacteria used for this purpose. Analysts in water microbiology laboratories can regularly culture and grow these coliform indicators without taking dramatic personal health and safety precautions. However, there do exist rare opportunistic strains among the coliform groups that can cause illnesses such as diarrhea, urinary tract infections and meningitis.
10. False. Organic chemicals are compounds of carbon, especially those in which hydrogen is attached to carbon. It was believed prior to 1828 that organic compounds could not be formed except by living plants and animals. However, in that year a 28-year-old German chemist, Friedrich Wohler, discovered by accident that application of heat to ammonium cyanate, an inorganic compound, caused it to change to urea, a compound that is organic in nature. Since then millions of synthetic organic chemicals have been created by man with thousands never-before-known new ones now being invented and registered with the Chemical Abstract Service each year. Plastics, resins, rubbers, synthetic fibers, membranes, solvents, pesticides, silicones and numerous other high polymers are examples of the synthetic organic chemical fields and their usefulness.
