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YPIE Scientist: Rania Khan

Research: The Effect of Sodium Hypochlorite (NaOCl) on Phytoplankton (Tetraselmis): A Controlled Version of a Combined Sewer Overflow Treatment

Awards: WESEF 2023: US Junior Stockholm Water Prize, Somers Science Fair 2022

Mentor: Joel Rodriguez and Jason Bonet

Research Location: Groundwork HV Science Barge


The research site in Yonkers, New York, employs a combined sewer system, which uses a single pipe drain to collect both rainwater runoff and wastewater from houses, buildings, and other structures. During dry weather, it functions as a separate system (with multiple drains for rainwater and wastewater), but during wet weather, too much water in one drain exceeds the dam limit, causing the water to overflow into the Hudson River. Environmentalists and the city of Yonkers collaborated to use sodium hypochlorite as a water cleaner to remove any fecal/harmful bacteria in 2003. Although sodium hypochlorite is effective at neutralizing fecal bacteria, it is believed to harm algae such as phytoplankton. We created a control version of the above-mentioned scenario for the research. Phytoplankton and hydro algal fertilizer were purchased, and the algae was grown for a month. Different amounts of 5% sodium hypochlorite concentration were added to phytoplankton batches, and numerical tests were performed. Weight and temperature changes were minor and insignificant. A hemocytometer (cell count) revealed a loss of up to 100,000 cells following sodium hypochlorite exposure. The PH level was 7 before dropping to 6 for 5 days before returning to 7 after 3 days. Finally, the color graph, which recorded the phytoplankton colors with RGB values, revealed that after sodium hypochlorite, the phytoplankton's dark green color changes to a dirty brown/yellow. This demonstrated that sodium hypochlorite inhibited photosynthesis by killing chlorophyll in phytoplankton. The color and cell count only return after almost 2 months, which is more difficult in the environment because more sodium hypochlorite is added after each rainstorm. This study demonstrates the harmful effects of sodium hypochlorite on algae and contributes to the growing body of evidence that this, among other factors, contributes to the rapid decline in phytoplankton population that is occurring in our environment.

About this Scientist:

Junior at Charles E. Gorton High School Rania Khan intends to pursue a career in medicine. She started reading more about environmental issues that were not given much attention in order to find out how CSOs harm nature, motivated by the expanding environmental issues like water pollution and climate change. In college, Rania wants to continue her scientific research.

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