EME 807
Technologies for Sustainability Systems

4.2. Mitigating Environmental Risk


Case of Dead Fish - Lake Ariel

Video Intro:

Another example we can look into is the chemical incident on Lake Ariel in Wayne County, Pennsylvania. In 2014, the owners of the land where the recreational lake is located, contracted a New Jersey company to help clean the lake of algae. Accelerated algae growth is believed to be the result of lake pollution due to illegal septic systems flushing their waste into the lake. The contractor applied two algaecide treatments of copper sulfate to the lake, which resulted in killing around 10,000 fish. Department of Environmental Protection issued a fine stating that copper sulfate applications should be spaced 7 to 14 days apart whereas the company made two applications spaced only 3 days apart. The owner argued that the extremely hot day during that summer was what ultimately caused the fish death. Nevertheless, the shortened time in between applications was considered negligence.

Check the links below to collect additional facts about this case, then work through a few questions to analyze the situation:

NBC News - Philadelphia

Pocono Record News

Probing question #1:

What do you think was the main risk the owners failed to mitigate in this case?

Click for answer.

Risk of losing aquatic life and thus decreasing the recreational value of the lake

Probing question #2:

What would you identify as a chemical hazard in this incident?

Click for answer.

Copper sulfate toxicity towards fish

Probing question #3:

What are the controls to be used to limit exposure in this case?

Click for answer.

The primary control is time for chemical application (that regulation was violated). Another control is the dosage of copper sulfate.

Probing question #4:

Based on the information available, what factor was primarily responsible for fish kill? Click on your answer below.

(A) Chemical exposure

The mass death of fish correlated with the chemical application - it happened 2 days after treatment, so it is easy to put the blame on it. However, there was an argument that the heat wave put extreme pressure on fish population limiting oxygen supply and thus caused the death. Both arguments are speculative.

(B) Heat

The mass death of fish correlated with the hot weather, so it was argued that it was the main cause. However that argument was biased as the owners tried to alleviate charges for irresponsible chemical application.

(C) Low Oxygen Content

Low oxygen can be caused by both excessive algae growth and heat. Possibly, both of those factors together kept the fish population under severe stress, although it might not cause the death. It was not the first hot day on record, and no dead fish was found until after the chemical treatment.

(D) Organic Water Pollution

Pollution present in the lake was the original cause of eutrophication, which might cause slow decline of fish population, but was unlikely to cause a sudden outbreak.

(E) All of the above

This would be most logical choice. With the high level of algae and heat, we can assume that fish population was under high stress and vulnerable. Copper sulfate attack was the final straw (the trigger) that pushed the system over the tipping point. It is likely that the combination of factors was responsible for the collapse.

Probing question #5:

What would be the optimal approach to the problem best aligned with the green chemistry principles?

  • (A) Strictly follow the protocol of copper sulfate application (7-14 days apart)
  • (B) Start with lower dosage of chemical and monitor the fish response
  • (C) Wait for a cooler day to perform treatment
  • (D) Minimize the septic tank flushing into the lake
  • (E) Leave the system as is and avoid using chemicals at all costs

Click for answer.

Answer D – minimizing septic run-off goes to the root of the problem. While it may take longer time for system to respond, this action follows Principle #1 Prevention, which eliminates the need to apply any dosage of chemicals, thus eliminating the hazardous exposure.
Other alternative measures could include: developing fish-tolerant chemicals to treat algae (Principles ## 3 and 4) and monitoring the health of the lake prior, during, and after treatment to tailor the application procedure to the specific ecosystem (Principle #11).

From this example, we see that dealing with sensitive ecosystems requires extra diligence when chemical flows are involved. Quite often certain aquatic species are only tolerant to a very narrow range of chemical parameters, such as ligand and metal concentration, alkalinity, and pH. Even small fluctuations may turn out lethal for sensitive species and can result in quick and irreversible ecological damage.

This example also provides an opportunity for exercising system thinking, during which we can try to establish multiple causal connections and understand the coupling effects, which are able to quickly amplify the ecological stress. In this case we observed it with the heat factor. Hotter temperature not only "purges" water of oxygen (due to lower solubility levels), but also promotes algae growth, which in turn removes oxygen from water even further. The system analysis can help reveal this sort of double impact, alert us of the increased risk, and prevent hasty actions.