In discussing "green" policies, the words "sustainability" and "pollution" are occasionally mixed together, as if they were antonyms. My gut feeling is that something that is polluting is by definition not sustainable, but I don't have a very clear view over the definitions of the two terms.
This question is inspired by a discussion at Politics.SE as to whether pollution can be sustainable.
Can a behaviour be polluting while still being sustainable?
Behaviour can be sustainable and polluting at the same time, if these conditions are met (all examples taken from wastewater):
The natural environment you are polluting is at all able to destroy the pollutants (usually, but not always, biological pathways): Taking a dump in a river may be okay, since your feces will be biodegradable. Other, industrial pollutants possibly not.
You pollute slower than the system you are polluting can destroy/digest the pollutants. Dumping the feces of whole town into a river will probably overload the ability of the ecosystem there.
You could state the last one differently: Pollution does not critically alter the ecosystem. Wastewater in rivers, lakes and the seas often consists of biodegradables that are in fact nutrition to parts of the ecosystem. But too many may lead to an algae-bloom, followed by a large scale die-off and eutropification of the lake, river or even patch of sea.
What you need to do is to understand the pathways of pollutants into and out of (defined broadly) the system in question, and try to quantify how much pollutants can be destroyed/degraded/transported out of your system. That should be your cap on sustainable pollution.
Note that almost always, a lot of polluters share the same sink for pollution - multiple cities along a river, and basically everyone breathes the same atmosphere. So to answer the question wether one single process is polluting sustainably, you must define how much of a shared sink can be "allocated" to this process. There is not always a straightforward answer to that.
"No" is a pretty safe answer in general to the question "Can a behaviour be polluting while still being sustainable?", just from any reasonable definitions of "pollution" and "sustainable".
But let's look at some corner cases.
For example, broadly speaking, CO2 is both a local and a global pollutant.
But.
If anthropogenic CO2 emissions were only 1-2% of what they are now, and not happening within urban areas, then natural carbon sinks could absorb those emissions sustainably, as long as those sinks are allowed to grow, rather than being shrunk.
And scientists such as Columbia University's Klaus Lackner have developed means of extracting atmospheric CO2, and we have the chemistry to turn CO2 into other chemicals, including methane. So there are round trips which would involve CO2 emissions, but which could be sustainable. Obviously the round trip would be a net consumer of energy, but the price of energy differs by time, place and form, so this can still be economically viable.
So, one way to look at the relationship between pollution and sustainability is this:
if there are procedures in place to reverse the pollution; and / or if the rate of release of pollutants is less than the sink rate of the environment, and if the pollutants' pathways from source to sink does not cause collateral harm on the way, then it could be sustainable. Otherwise, it is unsustainable.
I think pollution is part of the "cycle of life", so to speak. What is unsustainable is unmanageable amounts of pollutants.
To qualify as a pollutant in a scientific and practical sense, a compound or organism must exist in a kind of place and at a level that is considered toxic based on legitimate environmental science. For instance, when water is tested, there are acceptable thresholds for compounds such as lead.
The detection of pollutants at toxic levels when such levels were not detectable previously is a signal. The signal notifies environmentalists that an unsustainable industrial, business, or residential behavior pattern is emerging.
The toxic condition may be a transient caused by a single event, in which case it would disappear, or it may sustain. In may cases the toxicity would increase as populations rise or modernization continues.
In this last case, clearly the trend is toward the disruption of the life of those species for which the pollutants have reached toxic levels in that particular region. Assuming that the biosphere is largely symbiotic is a reasonable assumption, such disruption would ultimately increase risks in that region and others.
The cumulative effect of pollution in general can be inferred from this local analysis. If we consider sustainability as the reduction of risk to the geological, atmospheric, and biological processes that sustain life, then pollution reduces sustainability.
