By C.F. ’Chubb’ Michaud, CWS-VI
“Ashes to ashes, dust to dust.” We are all familiar with this oft-used phrase from the Book of Common Prayer (based on Genesis 3:19). Somehow, the author of these words had a unique understanding of the Laws of Conservation of Mass and Energy that wouldn’t be discovered for more than a thousand years. Man cannot create matter or energy from scratch. He can only change its form. Likewise, he can never destroy matter or energy. All the molecules will remain, albeit, in a different form of the exact same elements.
It all gets recycled
Take as an example the simple tree. It takes carbon dioxide (CO2) from the air, combines it with water (H2O) and through the miracle of photosynthesis (energy from the sun), releases oxygen (O2) and creates cellulose (C12H22O11), the stuff from which plants are made. We call it a carbohydrate. Starches and sugars are also carbohydrates and they all share the exact same chemical formula as cellulose. If we eat carbohydrates as a food source or burn the wood from that tree as a source of fuel, we recombine the carbohydrate with O2 from the air and send the CO2 and H2O back to nature whilst releasing the original energy of the sun as heat. Nothing has been gained. Nothing has been lost. That’s the Law.
Water is a great cleanser. We use it to wash our clothes, our dishes and ourselves. Mother Nature uses it to scour both land and sky. During the process, however, water can become contaminated.
Atmospheric moisture will condense on tiny dust particles before falling as rain or snow and it cleanses the atmosphere of built up gases (primarily carbon dioxide–CO2) in addition to oxides of sulfur and nitrogen (also acid formers) and other debris. “Pure as rain” is a bit of a misrepresentation. Rain is actually a dilute acid at a pH of around 5.5 and often containing up to 50 ppm of total dissolved solids (TDS) including calcium, magnesium, sodium, sulfate, chloride and silica (which is leached from dust particle) as well as bicarbonate and CO2. You have probably noticed that when rain falls on your freshly washed and waxed car, it leaves spots when it evaporates. After a few days of rain, the TDS drops to around 5 ppm, which is mostly as carbonic acid (H2CO3) –the combination of CO2 and H2O.
Most precipitation runs over the surface and collects in rivers, streams, ponds and lakes and is known as surface water. Some soaks in and becomes well or spring water, also known as groundwater. Excess CO2 tends to evaporate from surface containment so the water is closer to neutral in pH, generally lower in TDS, somewhat higher in dissolved oxygen and typically iron free with low hardness. Groundwater, on the other hand, is neutralized by the soil so is typically higher in TDS, hardness and whatever else is available from the soil. That’s the part that should have you concerned.
Earth’s crust, the part of the planet on which we live is 20 to 30 miles (30 to 50 km) thick but only makes up less than one percent of the Earth’s volume. It is composed primarily of metal and non-metal oxides (Table 1).
Metal oxides will form bases in water (Reaction 1) while non-metals tend to form acids (Reaction 2). These acids and bases further react to form other salts and water (Reaction 3). It is fortunate that the oxides (silica, aluminum and iron constitute nearly 85 percent) making up the surface of the Earth are sparingly soluble in water. Otherwise, we would all have fins. However, given a time span measured in hundreds of millions of years and the acidic nature of precipitation, elements are slowly leached from the crust and become a part of the groundwater.
The elements listed in Table 1 make up 99.6 percent of the bulk of Earth’s surface. It is what’s in the other 0.4 percent that gives us concern. 0.4 percent is 4,000 ppm and many of the other components of the crust make-up are toxic at only a few parts per billion!
Just because it doesn’t show on the water analysis doesn’t mean it isn’t there
When we review the list of common ions found in water, it includes calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), iron (Fe), aluminum (Al), bicarbonate (HCO3), chloride (Cl), sulfate (SO4) and silica (SiO2). Given the composition of the Earth’s crust (Table 1), we can readily confirm the leaching of inorganic mineral into ground water.
When we work on rating an ion exchange system, the components listed in Table 1 are often sufficient to get an accurate picture. After all, ion exchange doesn’t really care who its partner is. Each ionic equivalent gets to occupy the same amount of space and an analysis that covers 99.6 percent is plenty good enough. Often, the trace elements—those making up the other 0.4percent aren’t even listed. The ionic contribution of arsenic, lead, uranium and cadmium, for instance, may be less than 0.1 ppm (100 ppb). Even so, that water would be considered a toxic soup. It is the presence of those trace elements that really determine whether a given water source is potable or toxic. So…where do these contaminants come from?
Why do you think they call it dirt?
Not only are all 90 of the naturally occurring elements found in the periodic table found in the Earth’s crust (Figure 1), but all 90 can also be found in your water supply. Many are below the level of detection…but they are there. Many are considered toxic and we would call them contaminants. Much of the toxic element levels found in soil and groundwater are anthropogenic—a fancy word meaning ‘caused by man’.
Figure 1. Abundance of the elements in Earth’s crust1
Note that the data in Figure 1 is logarithmic and that the abundance of silica is set with a value of 106. All other elements are represented as relative to silica. For every 1,000,000 atoms of silica (106), there is approximately 1 atom (100) of molybdenum (Mo) or uranium (U). Gold (Au) exists at 1/1000ths or 10-3 atoms for every million atoms of silica. Rule of thumb says that for every increase of 10 in atomic number there is a correspondingly relative decrease in abundance by a factor of 10.
Of the 16 elements listed in Table 1 and making up 99.6percent of the Earth’s crust, only one (fluorine—usually present as calcium fluoride) is currently regulated on the US EPA’s list of (primary) potentially harmful inorganic chemicals. The US EPA secondary regulations list includes fluorine, aluminum, iron, manganese, sulfur (sulfate) and chlorine (chloride) among the common rock forming elements. For the most part, rocks are not very soluble in water—even acidic water. While we often experience treatable levels of naturally occurring arsenic, fluoride and uranium, it is unusual to find treatable levels of naturally occurring lead, cadmium, copper, zinc, selenium, molybdenum, antimony, chromium and others on the US EPA’s list. That’s because Mother Nature has had millions of years to clean up loose ends and most things that will dissolve are happily in equilibriums that are below the maximum contaminant levels (MCLs) for those elements (Table 2). Had things not happened that way, we might not be here. And…the way things are going, we are getting a second chance to wipe out mankind through carelessness.
Contrary to common belief, there is no such thing as pure water or clean dirt. All waters are simply dilute salts of various metals and all soil contains trace elemental metallic compounds. Ever since the invention of agriculture, man has been tweaking the composition of soil to improve his lot. Some of the tweaks are rather harmless such as the addition of ammonium salt as a nitrogen source. Some are non-issues such as the addition of calcium sulfate (gypsum) for pH control or sodium salt (NaCl) for moisture control. Others are not so friendly such as arsenic, lead and fluoride-based pesticides.
The two biggest contributors to excessive levels of regulated elements in soil and water are…man and …woman. We have met the enemy and he is us! While many trace metal contaminants can occur naturally, they are generally found at levels below the MCL. Over many years, through both neglect and ignorance of man and industry have used the back forty as a dumping ground and applied pesticides and fertilizers with no concern as to where they might end up. Smokestacks spewed millions of tons of arsenic into the air only to have it end up in the soil…and the water. In the 1930s, California sprayed lead arsenate on orchards at a rate of 260 lbs. of active ingredient per acre (US Department of Agriculture). That works out to over 100 ppm in the top six inches of soil (per season). Five decades of tetraethyl lead (TEL) as an anti-knock compound in gasoline deposited millions of tons of lead into the atmosphere and onto the ground. In 1979 alone, auto exhausts released 208.1 million pounds of lead into the air in the US. Lead from auto emissions is carried over 50 miles and distributed widely by wind.
Arsenic is contained in all soils and all water sources. Irrigation water is, therefore, an additional source of arsenic because when that water evaporates, it leaves the arsenic behind. Irrigation can deposit about 0.1 ppm per year of additional arsenic in soil. In fact, there is more of a contribution to soil contamination from irrigation than from fertilizer
Once in the soil and water, contaminants can be taken up by plants. The driving force behind the banning of TEL from gasoline was the concerns over the continued build up of lead in soil and agricultural produce. Lead is still used in fuel for aircraft and off road vehicles. Arsenic is still used in pesticides and wood preservation. Add to this the use of fluoride in pesticides and other agricultural sprays (plus the questionable practice of adding fluoride to the drinking water supply) and we have a persistent problem and an ongoing need for water purification for years to come. Dental fluorosis is on the rise even in areas that do not fluoridate their water supplies because of the extensive use in pesticides and its presence in irrigation water has resulted in excessive fluoride intake just from food2.
In general, the higher the level of contamination in the soil, the higher the likelihood of that contaminant showing up in the ground water. Contaminated soil leads to contaminated water. The containment of toxic substances deep underground, so called proper disposal, is but a temporary out-of-sight-out-of-mind fix. True to the parable, these substances will, one day, again join the soil and water from whence they came.
There is both a good side and a bad side to this factor. On the plus side is that should the source of contamination be halted, Mother Nature will eventually clean up the soil by having a constantly refreshed water supply pass through it. The negative side to this is that the movement of groundwater will move contaminants into other areas that may be more in the mainstream of urban living. This will lead to a shortage of cheap water and necessitate costly municipal and residential treatment.
The nature of dirt
Not apparent from the general composition of the Earth’s crust is what we might call the active ingredient in soil. Chemically, it is a sodium aluminosilicate or zeolite. There are more than fifty identified zeolites found to occur naturally3 and they vary widely in composition. They all have certain properties in common—they are all ion exchangers. Mined zeolites are typically in the sodium or potassium form (cation) and the Na+ and K+ ions are held rather loosely. This allows them to exchange with ions of higher charge—just like softeners. This unique chemistry of soil allows some contaminants to be far less mobile than others. One means of treating Cr+6 (an anion) is to chemically (or through the use of microbes) reduce it to Cr+3 (a cation), which is then immobilized by the soil. The same happens with lead, cadmium, copper, iron, manganese and zinc. Anionic metals (i.e., selenium, molybdenum, antimony, uranium, vanadium) are more mobile and show up down stream of the actual point of introduction.
And your point is….
There’s a reason your mother told you not to eat dirt! It can be pretty nasty. Soil contamination can occur through the natural erosion of rock but it is primarily caused by centuries of neglect and carelessness of mankind. Soil contamination is, in and of itself, problematic because it provides a source of heavy metals that can be taken up by plants. That puts those contaminants directly into the food chain. In addition, soil contamination leads to water contamination. This, in turn, leads to contaminated livestock, fish and fowl…all of which pass the contaminants on up the food chain and back to mankind (think mercury and sword fish). Is this the origin of the expression ”What goes around, comes around?” The problem is that a lot of people not responsible for the actions suffer the consequences.
Although the oceans are the eventual repository of all things discarded, the soil is the staging area. Atmospheric precipitation is acidic and as it passes through Earth’s strata, it takes a little bit of everything it touches along with it (including those corrosion proof burial containers). While nature provides a cleansing action, the water (and the aquifer) become contaminated.
Many common contaminants such as lead, arsenic and fluoride are accumulated by the body and even though not at toxic levels now, they may become so over time. For many of these contaminants, the only safe level for drinking water is zero. In addition, water is not your only source of these contaminants. Many are also found in the food we eat. Even organically grown produce does not guarantee chemical free because these contaminants are everywhere. Wastes that are dumped upon and buried within the ground do not stay put.
If you, as a water treatment professional, are intent on protecting the consumer with safe drinking water, you must also take the responsibility of approaching the customer with a good water analysis. Single digit ppb levels of heavy metals can be significant. Otherwise, you’d be guessing. We all know what’s out there and it does no good to bury our heads in sand (sand = soil = dirt). The water treatment industry has unlimited potential to both make a living and help people live.
- www.wikipedia.com, en.wikipedia.org/wiki/crust_geology
- Michaud, C.F., Fluoride–The Good, The Bad and The Ugly, WC&P, February, 2010.
- International Zeolite Association, Database of Zeolite Structure.
About the author
C.F. ‘Chubb’ Michaud is the Technical Director and CEO of Systematix Company of Buena Park, CA, which he founded in 1982. He has served as chair of several sections, committees and task forces with WQA, is a past director and governor of WQA and currently serves on the PWQA Board,, chairing the Technical and Education Committees. Michaud is a past recipient of the WQA Award of Merit, PWQA Robert Gans Award and a member of the PWQA Hall of Fame. He can be reached at (714) 522-5453 or via email at AskChubb@aol.com