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As much as 100kg of wet wipes enter the lower reaches of the Taff River annually, finds a new mathematical model.

Cardiff University scientists have developed the first comprehensive model that calculates wet wipe emissions to rivers and calculates how many natural fibers, regenerated fibers and plastic fibers per person are contributed to rivers annually. The research, "Predicting Flushed Wet Wipe Emissions Into Rivers," was in Water Research.

By integrating available data on flushed wet wipe disposal and their microfiber generation behavior with emission-based mathematical modeling, the Cardiff research team estimate that a subsection of the Taff River receives 100kg of solid wet wipes annually.

The research team also estimates that, on average, the amount of microfibers input to rivers in the lower Taff catchment annually is:

• 11,912 grams (or 6.5 billion fibers) of natural fibers per year
• 1,531 grams (42.6 million fibers) of regenerated fibers per year
• 2,670 grams (7.8 million fibers) of plastic fibers per year

Thomas Allison, Ph.D. researcher at Cardiff University Water Research Institute said, "Flushed wet wipes pose a significant pollution risk to river systems—from systematic impacts to impacts on water quality and introducing microplastics to our environment.

"However, the link between their emissions and environmental contamination remains unclear. Here we integrated emissions-based modeling with existing data on wet wipe disposal and microfiber generation to predict the quantity of emissions entering river systems and the transport pathways involved.

"Despite widespread public knowledge against the flushing of wet wipes, improper disposal remains a persistent issue. We need to thoroughly assess the environmental risks created by these flushed wipes. To do so, we need to know the quantities likely to enter river systems.

"Lack of quantified understanding of the journey of each wet wipe flushed down the toilet impedes proper understanding of wet wipes emissions to rivers, and ultimately to seas and oceans. Preventing the flushing of wet wipes is a key mitigation strategy, but understanding their transport through wastewater systems is essential for developing further targeted solutions."

The research team from the School of Biosciences, School of Chemistry and School of Engineering at Cardiff University have developed the first comprehensive model to accurately estimate wet wipe emissions to rivers by integrating available data on flushed wet wipe disposal and their microfiber generation behavior with emission-based mathematical modeling.

The researchers developed the wet wipe model by integrating microplastic emissions modeling with experimental models of wet wipe microfiber generation in wastewater systems.

The new mathematical model aims to map the entire journey of flushed wet wipes from wastewater systems to rivers, identify the main entry points of flushed wet wipes into rivers, estimate wet wipe emissions across both UK and EU rivers, and contextualize the impact of wet wipe pollution by comparing their river emissions with those of laundry microfibers.

The researchers found that while almost 99% of solid wet wipe emissions are transported to wastewater treatment plants and then directed to landfill and other facilities, wet wipes were still entering water systems.

The model exposed that wet wipe emissions to wastewater systems in the UK are substantial, with plastic wipes dominating solid emissions, and individuals contributing an estimated average of 33 plastic wipes annually, compared to four cellulosic wipes (eco-friendly and sustainable alternatives to traditional wipes).

On average, they calculated that 268,520 natural fibers, 1668 regenerated fibers, and 323 plastic fibers are emitted into water systems per person annually in the UK.

"Scaled up to the size of the Taff river, we see a substantial input to wastewaters of 7054 kg and 784 kg of solid plastic and cellulosic wipes. This is equal to approximately 1.5 million plastic and 165,000 cellulosic wipes flushed annually," said Dr. Benjamin Ward.

The new model identified nine pathways through which wet wipe emissions, both solid and microfiber, are transported, including wastewater to treatment plants, soil runoff to rivers, toilet misconnections to rivers, and sewer overflows to rivers.

"Toilet or kitchen misconnections are often overlooked as transport pathways for pollutants, yet our findings show that they can contribute up to 16 % of all solid wet wipe emissions to rivers," said Dr. Michael Harbottle.

"Our results also highlight the potential environmental risks posed by solid wipes and their microfibres in river systems. Further work is needed to refine our estimates, but in the meantime this work evidences a real need to develop targeted strategies to mitigate wet wipe pollution in our water systems," said Professor Isabelle Durance.