Call an expert today: +44 (0)114 272 2270
Free Environmental Bulletin: Subscribe now
Free Environmental Bulletin: Subscribe Email: info@em-solutions.co.uk Call: +44 (0)114 272 2270

CSOs and Microplastics

1 July 2021

Image of River

In our last blog on microplastics, we discussed what they are, how they impact the environment, and what we can do in everyday life to minimise their entry into the environment. In this blog we will look at how CSO (Combined Sewer Overflow) spills are contributing to microplastic pollution.

What is a Combined Sewer Overflow (CSO)?

A combined sewer system is a sewer system that uses the same pipe to collect rainwater runoff, sewage, and industrial wastewater. During periods of intense rainfall, the volume in the combined system can exceed the capacity and therefore, these systems are designed to occasionally overflow. The overflow systems are called Combined Sewer Overflows (CSOs). When CSO’s spill, they will discharge excess wastewater, which can contain untreated human waste, debris, and toxic substances into nearby waterbodies. CSO spills are a major pollution concern.

How do CSO spills contribute to microplastic pollution?

CSO spills lead to the release of often inadequately treated sewage into rivers but also the release of microplastics.

According to the WHO, the main ways that microplastics can enter waterways are through surface run off and wastewater effluent, and combined sewer overflows. (WHO) Combined sewer overflows are the points on sewer networks where wastewater gets into rivers. They are designed as relief valves on the system – if there’s too much water, they are allowed to spill. When a large quantity of rain falls in a short period of time or there has been heavy snow melt, to prevent sewers being overloaded, the combined sewers discharge into rivers. CSOs (combined sewer overflows) currently discharge in high enough quantities (and frequently enough even in periods of little or no rainfall) to pose serious issues.

Discharging untreated sewage leads to river pollution, plastic pollution, eutrophication, and affects the local ecology as the resulting drop in oxygen levels renders the water unable to support life.

Rivers are the main supplier of microplastics to the ocean. As mentioned in our previous blog, microplastic ingestion can cause digestive and therefore reproductive issues in aquatic life. Research has found that marine species are affected by microplastics in various ways and to varying degrees, for example the ingestion of larger microplastic particles in fish can diminish their startle responses.

Recent studies have also suggested that “biofilms” (functional communities of bacteria that build upon a surface) can form around these microplastics. Additionally, it may be possible for a genus of bacteria with pathogenic strains, Vibrio spp., to populate pieces of floating microplastics (Science Direct). Although more research is necessary on the long term impact of microplastics in our water, plastic pollution adds to a number of issues stemming from CSO spills.

This month is plastic-free July, have you taken the time to read part one of our series on microplastics? (EMS)

Recent Insights

MCPD Flow Diagram

MCPD Flow Diagram

Updated permitting requirements are still being overlooked by many businesses across the UK, potentially putting them at risk of prosecution by the regulators. Do you know whether you need to comply? Use our handy tool below to see if you need a permit.

National Marine Week 2021

National Marine Week 2021

The 24th of July to the 8th of August is “National Marine Week” and aims to encourage us to celebrate our seaside wildlife. In celebration of our marine life, local events are taking place along the UK's coast such as rock-pooling, snorkelling and even dolphin surveys, detailed on The Wildlife Trusts' website.

Fortnightly Bulletin - 19th July

Fortnightly Bulletin - 19th July

Our fortnightly bulletin provides you with news articles, legal updates, key dates and webinars from the environmental sector.

Bulletin Subscription

Subscribe to our FREE fortnightly Environmental Bulletin for news and updates on the environmental industry.

© 2021 Environmental Monitoring Solutions Ltd