Legacy pollution, an unfortunate inheritance

By: Dana Sackett

Legacy is defined as something that is inherited by one generation from the previous.  While some legacies are better than others, not all are good. Legacy pollutants are one of the bad ones.  These pollutants stick around to cause problems well after they are released into the environment. Indeed, they often continue to cause harm even after they are banned by regulation.  Legacy pollutants have three common attributes that make them particularly problematic: they are Persistent, Bioaccumulative, and Toxic (called PBTs for short). Infamous legacy pollutants include: polychlorinated biphenyls (PCBs), dioxins and furans, lead, methylmercury, chromium, and some existing and banned pesticides.

Source: http://www.michigan.gov/mdhhs/0,5885,7-339-71548_54783_54784_54785_54800-256866–,00.html

The first characteristic, persistent, is obviously problematic because they do not break down or decompose easily in the environment.  Not as obvious, but a natural consequence of being persistent, is that they can travel great distances (even globally via equipment, products, food, or natural forces) as they continue to cycle through the environment.  This allows remote ecosystems that are far from the source of a legacy pollutant to be contaminated. Persistence is often measured by determining the half-life of a pollutant, which is the amount of time it takes for half of an amount of the pollutant to degrade.

One way persistence is measured is half-lives shown above. For a pollutant to be considered persistent it generally requires a half-life greater than 2 days in air, 2 months in water, and greater than 6 months in soil and sediment.  However, many persistent contaminants have half-lives greater than 10 years.  One even has a half-life so long that we have been unable to observe it degrade in the environment at all (see https://thefisheriesblog.com/2014/10/05/as-it-turns-out-what-we-dont-know-can-hurt-us/). Source: http://npic.orst.edu/factsheets/half-life.html

Bioaccumalative is the second common characteristic of legacy pollutants.  This concerning characteristic is because many legacy pollutants do not dissolve in water but instead combine with or dissolve in fats (chemicals that do this are called lipophilic).  This makes these pollutants resistant to environmental degradation and also allows them to easily bioaccumulate in food chains.

PBTs accumulate as bigger animals eat smaller animals. Animals at the top of the food chain, like orcas, end up with the highest concentration of PBTs.  https://ecology.wa.gov/DOE/media/Images/WASTE-TOXICS/Reducing%20toxic%20chemicals/Chemicals%20of%20concern/PCBs.jpg

Beyond being persistent and bioaccumalitve, the third defining characteristic of legacy pollutants is the most alarming: they are toxic at very low concentrations.  The individual toxic effects of these contaminants are also generally well known and wide ranging for fish, wildlife, and people.  Adverse effects have been noted to impact nervous, reproductive, endocrine, and immune systems; with many also being strongly carcinogenic.

Original 12 Key POPs—the Dirty Dozen.jpg
A common type of PBTs are called persistent organic pollutants or POPs.  The big 12 POPs or dirty dozen were listed by the Stockholm Convention in 2001 (a global treaty which calls for the phasing out and elimination of these particular contaminants worldwide).  However, more pollutants have been added to this list in recent years

Legacy contaminants are often used and widespread before we identify the full extent of the damage they can do to the health and well-being of our fish, wildlife, and environments as a whole.  This is why regulations and programs that prevent the discharge of these legacy pollutants are so important.  The US Environmental Protection Agency is responsible for evaluating the associated risks of new and existing chemicals; ensuring they do not have these troubling characteristics.  The USEPA is also responsible for finding ways to prevent or reduce pollution from getting into the environment through programs under the Toxic Substances Control Act and the Pollution Prevention Act.

Simplified example of how a persistent pesticide can cycle through the environment.  Source: https://www.intechopen.com/books/applied-bioremediation-active-and-passive-approaches/persistence-and-bioaccumulation-of-persistent-organic-pollutants-pops-

Legacy pollutants are inherently a risk to future generations.  This is why the recent loosening of environmental regulations (for example federal cutbacks in environmental protection policies and programs) is a concerning trend.  Even a short few years of deregulation could have impacts that affect generations to come.

Resources and References:

Gramatica P, Papa E. 2007. Screening and ranking of POPs for global half-life: QSAR approaches for prioritization based on molecular structure. Environmental Science and Technology 41:2833-2839.

Hutchinson TH, Lyons BP, Thain JE, Law RJ. 2013. Evaluating legacy contaminants and emerging chemicals in marine environments using adverse outcome pathways and biological effects-directed analysis. Marine Pollution Bulletin 74:517-525.

McGoldrick DJ, Murphy EW. 2016. Concentration and distribution of contaminants in lake trout and walleye from the Laurentian Great Lakes (2008-2012). Environmental Pollution 217:85-96.













Please leave a thought provoking reply. We reserve the right to remove comments deemed inappropriate.

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s