Now that I have discussed microbes and how they can be killed or have their growth stopped with the use of specific and non-specific compounds, and the types of communities microbes will form in a pond (no microbe is an island – biofilms), I would like to elaborate on cleaning and how it is important to know all about a chosen product or chemical and goal when wanting to clean. This applies to all situations in which you may want to lessen the number of microbes and thus clean a surface or area.
First, there are three large terms used for cleaners that should be clarified. It is important to know what these terms mean when selecting the proper product for the job. The first term used is sterile, or to sterilize. This is the most severe form of ridding microbes. It is actually when all microbes and life are removed and killed. All the cleaners you will buy cannot accomplish this task (as I mentioned in my first post, it is nearly impossible to remove all microbes and it is unnecessary). Only special facilities are equipped to do this, such as hospitals and labs like the one I work in. Only when doing sensitive experiments in biology or science and when using tools to treat illness, like performing surgery, is it even worth considering obtaining sterile tools and conditions. Otherwise, when considering all other aims, like household cleaning and pond maintenance, the aim is disinfection. Disinfection, or a disinfectant, is the second term. To disinfect is not to remove all microbes but to remove many microbes that may cause a problem. In fact, many commercially available disinfectants, as determined by standard testing methods, will be able to reduce microbial contamination by several orders of magnitude. The third term is an antiseptic, these are like disinfectants, but they are substances that are used on living tissue to remove problem causing microbes. One example of these is iodine when it is applied to the skin to reduce infection in an injury. All antiseptics disinfect, but not all disinfectants are antiseptic. Some disinfectants are very toxic and, therefore, you would never want to apply it to living tissue like your skin.
The disinfectants exist in a wide array of groups on which I will elaborate. Depending on the goals set out for cleaning, the choice of a disinfectant may differ. Disinfectants differ in their cost, toxicity, how quickly they break down, what sort of surfaces a disinfectant may best clean and how effectively they kill certain microbes. Disinfectants are not selective like the antimicrobials (I went over this in the first post) but, depending on how you use them, they may be more effective at killing a specific type of microbe.
1. The alcohols (ex: ethanol): These can be used as antiseptics as well. They are non corrosive but may be a fire hazard, since they are highly flammable. It can be difficult to get the full disinfectant efficacy because alcohols evaporate quickly. In other words, they have a limited residual activity. It is important to remove excess biological material (organic material) before using these disinfectants because their presence will limit the activity of the disinfectant. Higher concentrations are not necessarily the best because the alcohols diffuse better through cell membranes diluted to 70% with water, though higher concentrations have been shown to work better with certain kinds of viruses.
2. The aldehydes (ex: formaldehyde and gluteraldehyde): Some bacteria have the ability to form an extremely robust form of protection against the environment called a spore. A lot of disinfectants are useless against bacterial spores. The aldehydes have a wide spectrum of microbes they can kill including bacterial spores and fungi. Disadvantages include that they are quite toxic, partially inactivated by organic material and only have slight residual activity.
3. The phenolics (ex: phenol): This disinfectant group contains the first disinfectant discovered by Joseph Lister in 1867 and was employed first in surgeries. This disinfectant is known as phenol, or was then known as carbolic acid. The disadvantage to this disinfectant is that it is corrosive to skin and can react with some plastics. The advantage to these disinfectants is that they have a broad range of microbes that they can kill.
4. The quaternary ammonium compounds: These compounds can kill algae (algaecide) but have a short 24 hour life span until the compounds break down and are no longer effective.
5. The silver compounds: Depending on the pH in which the compounds are being used, they can last several weeks. These compounds are capable of killing algae and bacteria. One disadvantage is that if the compounds are exposed to a high pH and sunlight, they may stain some surfaces.
6. The oxidizing agents (ex: bleach, chlorine, hydrogen peroxide, iodine, ozone): These compounds include several disinfectants that are quite common in everyday usage and have many different ways in which to be effective, so I will discuss them in a little more detail. Some of these compounds, such as iodine and hydrogen peroxide, are safe enough to use on the skin as antiseptics. While others, like sodium hypochlorite or bleach, are caustic to the skin, lungs and eyes but, when diluted enough, is safe enough to be in our drinking water. Therefore, bleach especially demonstrates how, depending on the situation, a disinfectant may produce different results. At the low concentrations in drinking water, however, it is not effective at killing algae. At higher concentrations, like a 5% solution, it is effective against many common pathogens including M. tuberculosis (the bacterium that causes tuberculosis), hepatitis B and C (viruses that cause hepatitis), and, in this case, will be effective against algae. Bleach acts by attacking lipids (fats) in cell walls and then proceeds to destroy enzymes in the cell by oxidation reactions, which are defined as chemical reactions where there is a loss of electrons. The compound of sodium hypochlorite in bleach is not a good disinfectant. It must be dissolved in water to form the product called hypochlorous acid (HClO), which is the true disinfectant.
Figure 1: The dissolving of sodium hypochlorite (NaClO) in water (H2O) to create the disinfectant called hypochlorous acid (HClO) and sodium (Na+) and hydroxide (OH-) ions. The arrow indicates the chemical reaction between the reagents of sodium hypochlorite and water to create the two products of hypochlorous acid and the sodium and hydroxide ions.
NaClO+H2O → HClO+Na++OH-
Bleach is also good because it is relatively safe to use in the environment. This is because it will quickly break down into salt (NaCl) and oxygen (O2), which are not harmful. The disaavantages of bleach are that it requires 30 minutes of exposure to kill bacteria and if it is mixed with ammonia or any other acid, such as vinegar, it will cause harmful gases to form. Bleach, like other disinfectants, is less effective if organic material is present.
The overall message to be taken here is that there are a variety of disinfectants that can clean your home or pond but, depending on each situation, some cleaners will work better than others. Even the manner in which a single type of disinfectant is used may help or hinder its effectiveness. Important factors to consider are the mode of action of a certain type of disinfectant and its spectrum of activity against different types of microbes. With that known, then one must consider what types of microbes pose the problem and need to be reduced in number. In the case of ponds, the problem microbe will often be algae, which I will discuss in my fourth post (Phycology: The Forgotten Field of study and the Pond). Then one must employ the disinfectant in a fashion that assures will maximize the benefits of the compound, which include a proper concentration, time of exposure and the right surfaces and environments which will pose no problem to the use of said compound. An example of this is that some disinfectants are corrosive to certain surfaces. Here at Village Pond and Garden, if you have a pond that is not looking its cleanest, we will employ various techniques to see which microbes are causing the problem and how to best minimize their numbers by verifying the environment of the pond and by employing disinfectants, if necessary, in a way catered to your pond. Once all of the variables in a home or pond are known, then disinfecting agents can be used to their maximum potential.
• There exist three terms that globally encompass types of cleaning. To sterilize, disinfect and an antiseptic.
• Sterilize is to completely kill all microbes. Disinfect is to greatly reduce the number of problem microbes. Antiseptics are disinfectants used on living tissue.
• Disinfectants exist in a wide array of groups, which differ in their mode of action and spectra of microbes to which they are effective (alcohols, aldehydes, phenolics, quaternary ammonium compounds, silver compounds, and oxidizing agents).
• Due to the differences in disinfectants, it is important to choose the correct one that will have the most benefits and least drawbacks for the specific job at hand.
• Factors that may affect a cleaning job and choice of disinfectants include cost, toxicity, how quickly they break down or evaporate (residual activity), which surfaces are best suited for a certain disinfectant, concentration and time of contact.
• Disinfectants can be used to their maximum potential once all variables in cleaning a home and/or pond are known.