In a previous article, we discussed about how scientists and engineers use simple, elegant mathematical models called Mass Balances to determine the amount of pollution in an ecosystem.  In this article, we’ll delve into the complexities of mass balance equations and take a closer look at how they apply to the natural world and our interaction with it.

First, let’s recapitulate what we already know. A Mass Balance equation states that the following is true for a given closed system:

(Mass Input) – (Mass Output)

=

(Accumulated Mass) – (Mass Produced from Reaction)

A select few systems, such as elements participating in nuclear fusion, deviate slightly from this rule due to a phenomenon called loss of mass. However, that’s not the case with macroscopic systems, which are the focus of environmental science. Scientists and engineers studying those systems investigate other phenomena, such as chemical and biological reactions, and changes in phase.

But what happens when no reactions take place? Although this somewhat simplifies the system in question, we often depend on chemical and biochemical reactions to address pollution in the first place. For instance, there are novel technologies that take advantage of a pollutant’s properties to absorb it into a porous material or make it react with another chemical to form less harmful compounds. In the fossil fuel industry, a process called the Water Gas Shift reaction is used to convert toxic carbon monoxide into carbon dioxide and hydrogen, and has multiple applications in hydrogen-based energy technologies.

There are also examples of pollution happening precisely because a pollutant has been discarded into a non-reactive ecosystem. That is the case with plastic pollution; plastic is very durable, which unfortunately means it is virtually impossible to biodegrade by natural means, at least in a timeframe that is meaningful to our ecosystems and lifespan.

Let’s look at this in numbers: according to Our World In Data, 7.08 billion tonnes of plastic were discarded in 2015. If the system we’re examining is the Earth, that number is the cumulative mass input of plastic waste into the biosphere. Of this, 25.5% was incinerated and 19.5% was recycled – combined, those percentages constitute the mass output. The remaining 55% (a staggering 4 billion tonnes) is the accumulation. Unfortunately, while recycling, upcycling, and plastic sequestration technologies grew in popularity between 2010 and 2015, so did plastic production, resulting in a 7.1% increase in plastic accumulation.

 

Once again, it’s important to remember that mass balances are merely the foundation of pollution modelling. As with all kinds of pollution, the origins of the plastic that litters our oceans, as well as the pathways and speed at which it finds its way there are difficult to determine. It takes an intimate knowledge of human and corporate activity, economics, and even geopolitics to address and manage waste holistically. The takeaway from this discussion should be that even though scientific knowledge can appear unattainable, it is founded upon concepts that are accessible to everyone, provided they receive guidance and invest effort as needed. Anyone can care about the environment – and with the resources we have available today, anyone can do their best to better understand the phenomena behind climate change, pollution, and other environmental issues.