Microplastics, mostly fibres, found in mangroves in southwestern India

Photo by Saumitra Shinde/Mongabay.

  • Scientists have found various forms of microplastics in surface water samples from the Kota mangrove in Karnataka.
  • Microplastic fibres were the most abundant, followed by films, fragments and foam.
  • The concentrations were the lowest during the monsoon season, possibly due to outflow to the Arabian Sea.

A new study from India describes the type and distribution of microplastics detected in a mangrove in south-western India, offering fresh insights into the extent of infiltration of these contaminants, described by the United Nations Environment Programme as one of the “long-lived legacies of plastic pollution.”

Fibres, mostly measuring less than a millimetre, emerged as the most abundant category across all samples studied from the mangrove in a coastal village Kota in Udipi district of Karnataka state, by researchers from the Manipal Institute of Technology and Universidad del Atlántico, Colombia.  The mangrove forest at Kota is about three kilometres long and has over 10,800 people residing there.

Previous studies from Asia also have shown the prevalence of microplastics in mangroves in Asia which is home to 42% of mangroves. A study from China in 2020 reported dominance of foams and fibres from mangroves in China.  Another study from Thailand showed pollution of the mangrove sediment in the Mae Klong river basin, an important fishery site in the upper Gulf of Thailand, with microplastics and microparticles, mainly chemicals used in the textile industry.

But there is scant data on their occurrence and distribution in mangrove ecosystems specifically from south-western India.

The scientists in the Kota study used a combination of field sampling, laboratory analyses and statistical methods to study microplastics in the mangrove, to identify the types of microplastics and understand their potential impact on the mangrove ecosystem.

They found all categories – from fragments to foam, fibres, films and pellets – in surface water samples from the Kota mangrove. Fibres were the most abundant, followed by films, fragments and foam.

The scientists report that the concentrations were the lowest during the monsoon season, which could be attributed to enhanced flow rates, which facilitate the transport of microplastics from the mangroves to the Arabian Sea. The higher levels seen post-monsoon could due to tourism activities.

“The present study provides an in-depth examination of microplastic pollution in the tropical mangrove ecosystem of Kota, south-western India, incorporating ecological health perspectives,” the study says.

Percentage of different categories of microplastics recorded from water samples in a study in the Kota mangrove ecosystem in Karnataka. Image from “Seasonal variation of microplastics in tropical mangrove waters of South-western India” by Valsan et. al.

The researchers say that the outcomes are expected to inform local and regional policy decisions and provide actionable insights for the conservation and sustainable management of mangrove ecosystems.

Also, “the findings of this study could serve as a model for similar ecosystems globally, highlighting the necessity for unified action against plastic pollution in marine environments,” the report says. “We also explore the factors influencing these changes and the associated risks to regional biodiversity. This research aims to contribute to several UN Sustainable Development Goals, for example, SDG-6 on water and sanitation; SDG-14 on life below water, and SDG-12 on responsible consumption and production.”

Limited studies

Previous studies from India have not focused on the seasonal distribution microplastics, Anish Warrier, assistant professor at the Centre for Climate Studies at Manipal Institute of Technology, Manipal, and one of the authors of the report, explained to Mongabay-India. “In our work, we observed that the microplastic load was greater during the post-monsoon season than during the monsoon season. This could be due to the increased flow rate during the monsoon season, which transports microplastics away from mangroves into the Arabian Sea.”

The scientists noticed a significant increase in the microplastic load, which they attributed mainly to “the unscientific construction of a bund.”

“This bund obstructs the hydrodynamic conditions, leading to an increase in the load of microplastics in the water,” says Warrier. “We observed various heavy metals adhered to the surface of microplastics. These heavy metals could potentially leach into the environment, increasing the ill effects caused by microplastics on the biota.”

The team also observed that microplastic pollution is more prevalent where there is increased anthropogenic activity. “It could be due to mismanaged debris or fishing activities,” says Warrier.

It is important to have a regulatory framework at the local level to ensure proper disposal of plastic waste. Additionally, good outreach initiatives to residents on the extent of microplastic pollution and its detrimental potential on their livelihoods as those who depend on resources from these mangroves, the report says. “These forests are crucial in all aspects and must be protected from being destroyed due to human activities.”

Representative image of plastic in a mangrove in Mumbai. The presence of microplastics in mangroves is mostly attributed to the type of anthropogenic activity in the region and may be different for different areas. Photo by Saumitra Shinde/Mongabay.

Other scientists also agree on the paucity of such studies, given the importance of such data.

“The microplastics in aquatic ecosystem will be consumed by the aquatic organisms like fishes and other fauna which will be affecting their metabolic processes,” says R. Ramasubramanian, senior fellow, coastal systems research, at M.S. Swaminathan Research Foundation, Chennai. “There are not many studies in mangrove wetlands and these studies are important for the urban areas like Mumbai where large amount of plastics and dumped near the mangrove wetlands.”

“Only limited works are available for microplastic pollution in the mangrove areas of India especially in coastal Karnataka region,” says Kathiresan Kandaswamy, director of the Centre for Advanced Studies in Marine Biology at Annamalai University. Microplastics pollution in Indian mangroves is a growing issue in the mangroves of high tourist attractions, which can be controlled.

That said, extrapolating the Karnataka study findings to other areas may not be entirely accurate, the scientists say.

“It is important to note that the presence of microplastics in mangroves is mostly attributed to the type of anthropogenic activity in the region, so extrapolating our findings to other mangroves may not be accurate,” says Warrier. “One should also consider the river where the mangrove is located and what activities take place in the upper reaches of the river.”

Microplastics can be transported upstream and enter mangroves when there is a reduction in the flow velocity due to the thick network of roots and vegetation in mangroves, explains Warrier. Additionally, the location of the mangrove also affects the distribution of microplastics. For example, the microplastic distribution in mangroves developed along the estuary will be different from that in deltas.” Nevertheless, mangroves are considered sinks and sources of emerging contaminants like microplastics, which is true for all such forests within India,” he adds.

Kandaswamy says the findings cannot be exactly extrapolated and it depends upon several factors, such as the changing tourism activities, human interventions, as well the type of mangroves such as delta, backwater and island systems.

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Future direction

Warrier says that his team, after detecting microplastics in water, is currently quantifying the microplastics in the biological organisms of the region. “As the region has economically important species that are exported from India, it is important to understand the presence and distribution of microplastics in various compartments of fish and crabs,” he points out.

It is important to address how microplastics move up the food chain and bioaccumulate at different trophic levels, says Warrier. “We are trying to understand whether there is a change in the behaviour of microorganisms in the environment by comparing the ones present on plastic with the ones present on natural substrates like rocks. Once we have microplastic data from all the important sources, such as water, sediment and biota, we will focus our research on devising policy-related scientific articles that could be used by relevant authorities to curb microplastic pollution.”

It is necessary to create more action-oriented awareness among people about the seriousness of plastic pollution, says Kandaswamy. “The microplastics are reportedly present even in the marine table salts used for human consumption, although the impact of microplastics on human health is not clearly understood.”

The use of plastics can be better prevented, but those already used in the past will continue to cause impacts which cannot be controlled, adds Kandaswamy. “The increasing concern of microplastic pollution in every component of our environment is being globally explored, with relatively fewer studies in India. It is a matter of necessity to understand the extent of microplastics pollution in our country.

Read more: Unpacking the presence of microplastics in the Bay of Bengal


Banner image: Representative image. Microplastics in mangroves at Carter Road in Mumbai. Photo by Saumitra Shinde/Mongabay.

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