Yesterday, I was called on the phone by my senior brother and friend; Mahmoud Nurudeen of Joy Fm who asked whether or not I've seen the news about River Tano acid pollution after a track carrying car batteries accidentally slipped into the river.
After reading the story, I have decided to throw more light on the probable reason why local authorities have advised that residents should not drink the water for the period.
Basically, the story said the river was polluted by acid and this isn't strange. Often we hear of water pollution by acid from mines especially river waters.
First of all, rivers get polluted naturally by other factors aside from direct human influence. One is by the result of acid rain. Again, water bodies can be acidified when there is too much of dissolved carbon dioxide in the water. This can react with the water to form carbonic acids. Low levels of water algae and water plants can reduce photosynthesis, increasing carbon dioxide concentration in the water.
What we need to understand is that in every habitat, there must be equilibrium to stabilize the environment. In order to maintain equilibrium in water bodies, pH is one of the factors that play a very key role in this.
Just like temperature, pH (which stands for the power of hydrogen) is determined on a logarithmic scale of values universally ranging between 0 to 14. pH isn't something you can see physically. It defines how acidic or basic a substance is (in our case, the water).
When we record pH less than seven, it is said to be acidic. The smaller the number, the high the acidity. Likewise, numbers above seven are basic or alkaline. The higher the number, the higher the basicity or alkalinity. At a pH of 7, it is said to be neutral (eg: pure water. NB: pure water isn't the high particulate filtered water we drink each day from bottles and sachets. In fact, they are not pure water).
When determining pH say on the acidity scale (6.9 and below), as the number decreases, it means the number is ten times acidic than the previous number. Likewise on the alkaline scale (7.1 and above). As you climb up, each number is ten times basic than the preceding number.
Acidity is determined by a higher concentration of H+ in the water. On the contrary, the high the concentration of OH¯, the more basic the water will be.
Our water bodies get acidic or basic each day by national phenomena. However, in the natural ecosystem, there are some factors that keep the water in equilibrium. For instance, during acid rains or when there are carbonic acids in the river, the limestones at the bottom and sides of the river will serve as a buffer. They'll then try to neutralize the reaction by pushing it towards the alkaline range. This is why our water bodies are still safe.
pH plays a very important role in water bodies in that it creates comfortable environment for the species in the water such as algae, crabs, fishes, turtles, frogs, shrimps, etc.
When algae and other plants undergo photosynthesis, they utilise hydrogen which increases the level of pH. Another factor is respiration and decomposition which on the other hand, decreases pH levels.
Alkalinity plays a role in buffering these changes in our water bodies. Therefore minor fluctuations in the water do not affect the water that much.
WHAT CAUSED THE POLLUTION
It will be interesting to note that car batteries mostly have a pH of approximately 0.8 at 4.2 to 5 mol dm^–3 concentration. Meaning pH less than 1. The acid that is fused in lead-acid batteries have about 30 to 50% of sulphuric acid (one of the strongest acids) in it.
The acid in car batteries is strong enough to corrode one's skin. It is very dangerous even when it touches clothes, it eats it.
Unlike the normal pH in our waterbodies and slight pH changes, the case of the high conc sulphuric acid will be easy to be buffered, unless it takes some time before the river will attain equilibrium and diluting the concentration to levels that are safe.
The alarming issue is the volume of acid that was diffused into the river. If it was just a mere small volume, the alkalinity of the river could easily take care of it.
ADAPTABLE pH FOR WATER ECOSYSTEMS
Due to the bedrock in rivers, streams, freshwater lakes and ponds, the pH ranges from 6 to 8.
While ideal pH levels for fish are 7-8 (fish blood has a pH of 7.4) ²⁰, most fish can adapt to the pH level of their environment (6.0-9.0) as long as there are no dramatic fluctuations. A dramatic fluctuation is considered a shift in pH of 1.4 (up or down) ²². For saltwater fish, the pH of water should remain between 7.5 and 8.5 ⁹.
pH in the Natural water bodies
Ideally, the optimum pH for fishes ranges between 6.0 and 9.0 and it will continue to thrive well if there's no shift in pH of about 1.4 above or below the optimum level. Salmons require pH between 7.0 and 8.0. pH below 6.0 will severely kill them due to potential uptake of heavy metals such as cadmium, mercury, lead, etc. often from mining activities.
However oceanic organisms such as the clownfish and corals require higher pH levels. Corals require calcium carbonate, hence pH below 7.6 will kill them. Running water from mines will lower the alkalinity of the water due to their acidity making it acidic. In this situation, fishes won't be able to survive. Mostly it is frogs and other amphibians who are able to survive at such conditions. They can live in conditions even at a pH of 4.0.
Normal rainwater and snow have pH of approximately 5.6. Even though this value is acidic, its acidity is less to affect living organisms in the water bodies. Seawater has a pH around 8.2 but can vary between 7.5 and 8.5 based on the salinity of the sea. Higher salinity will make the water too basic. Organisms are able to live in the sea due to its ability to buffer free hydrogen ions in it.
About the writer
Zakaria Abdul-Hakim is a final year Biotechnology and Molecular Biology student at the University for Development Studies. He is a budding student researcher, Climate change enthusiast, writer, freelance journalist and activist.
He is passionate about science and technology and communication scientific knowledge for the layman understanding.
For further reading on pH and water acidity, refer to the below literature;
◾Fondriest Environmental, Inc. “pH of Water.” Fundamentals of Environmental Measurements. 19 Nov. 2013. Web. https://www.fondriest.com/environmental-measurements/parameters/water-quality/ph.
◾"pH and Taste - Chemistry LibreTexts" https://chem.libretexts.org/Bookshelves/
◾What Is Battery Acid?" https://www.thoughtco.com/what-is-battery-acid-603998