Low tide, high on trash: New study identifies flow of plastic into the sea

A first-of-its-kind study carried out in Mumbai to understand the flow of plastic waste into the Arabian Sea has revealed that through a Juhu water channel alone,

A first-of-its-kind study carried out in Mumbai to understand the flow of plastic waste into the Arabian Sea has revealed that through a Juhu water channel alone, 26 times more waste, including plastics, is carried during low tide as compared to high tide.

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Finding of the study ‘Quantitative assessment of influx and efflux of marine debris in a water channel of South Juhu creek, Mumbai,’ conducted by ICAR-Central Institute of Fisheries Education (CIFE), Versova, were published recently in the international peer-reviewed journal Regional Studies in Marine Science.

“Low tide is of a longer duration as compared to high tide. Though the depth of the water column is less during low tide, water in the channel is constantly flowing towards the sea, carrying with it a lot of debris,” said SP Shukla, co-author and principal scientist, aquatic environment and health management division, ICAR-CIFE. “We found that only a fraction of plastic returns to land during high tide as compared to the quantum that goes into the ocean.”

To date, a majority of studies quantify marine debris and plastic items through beach surveys – either settled on beaches or floating on the surface of the open sea and coastal waters.

In the present study, a six-member ICAR-CIFE team placed their newly-designed entrapment device in the water channel to gather data about the unregulated transport of plastic and debris into the sea through connected water channels. CIFE is seeking a patent for the entrapment device.

Over five months, 65.42% higher quantity and 136.95% increased weight of plastic materials was collected during low tide conditions – 3,437 plastic items weighing 130.87kg during low tide as compared to 2,078 items weighing 55.31kg during high tide. The device also collected other marine debris flowing from the landward side during low tide and seaward side during high tide.

Researchers said the baseline data is the first report on the influx and efflux of plastic through marine debris from a water channel to the sea under tidal influence.

Shukla said the device measuring 2 metres was placed in the 10m-long water channel, and therefore, the total quantum of plastic would be five times more than what the study found.

Researchers said policymakers should identify potential areas of estuaries, creeks, and rivers connected to the sea carrying huge loads of plastic debris so that managerial solutions to the problem can be tackled.

“One way of doing so is by installing the entrapment device. Imposing stringent judicial management action against plastics items and decreasing the industry turnover against plastic production, and raising public awareness, are some other measures that can be undertaken by policymakers,” said Manickavasagam S, principal investigator (formerly of CIFE) and scientist, Ocean Information and Forecast Services Group, ESSO-Indian National Centre for Ocean Information Services.