Chemical tests carried out, as part of a project submitted for the RDS Dublin event, showed elevated nitrate levels in Courtmacsherry Bay and nearby Broadstrand beach.
“This could indicate contamination by agricultural runoff, fertiliser or household waste,” said the girls’ teacher at St Brogan’s College, Bandon.
Karen Keohane, who teaches chemistry and maths at the school, said the two second-year students had approached her with the idea for the project after hearing the story of a dog which had died of water-borne E.coli.
It was believed the animal contracted the disease after paddling in Courtmacsherry Bay, she said.
A series of tests carried out by St Brogan’s College classmates Emma Kelly, 13, and Rachel Lordan, 14, on samples of seawater near two open sewer pipes at Courtmacsherry beach, found elevated levels of nitrates compared to samples taken from neighbouring beaches at Dunworley, Harbour View and Garrettstown.
The girls’ tests showed samples from Courtmacsherry Beach had nitrate levels up to 15 times higher than samples from the other three beaches.
“This water from the sewer pipes was flowing directly onto the beach and into the sea where people are swimming,” said Ms Keohane.
She said the pH of the water at Courtmacsherry was higher than at Dunworley, Garrettstown and Harbour View beaches.
“Sewage is the main source of excess nitrate added to natural waters, while fertiliser and agricultural runoff also contribute to high levels of nitrate,” she said.
She said Emma and Rachel planned to send their findings to Cork County Council and the EPA following the BT Young Scientists Technology Exhibition. The students also plan to talk with the community in Courtmacsherry to help raise awareness of the findings.
Meanwhile, the pair also examined an open sewer pipe at Broadstrand beach. Water from the pipe was flowing directly onto the beach where students saw people swimming.
Tests at Broadstrand showed an elevated level of nitrates up to 14 times higher than Dunworley, Harbour View and Garrettstown beaches.
The level of phosphates from Broadstrand, where the open pipe was located, was also higher than at Courtmacsherry and also at their three.
The findings could indicate runoff from household detergents or fertilisers, said Ms Keohane.