“So, what happens with your Biosafety Level 3 lab waste?” I asked the laboratory manager. “Our safety assessment says to just mix it with sterilant and wash it down the drain – there is worse stuff down there already.” “How about genetically modified material?” “Yeah, that goes the same way - It’ll die in the drains”. 

Treating biologically hazardous waste in such a way is not uncommon in the UK – the combination of chemical sterilants and a well-developed system of sewerage and treatment plants can handle a wide range of biologically active substances, but it is not a failsafe system.

The 2007 foot-and-mouth disease outbreak within the county of Surrey, UK, is believed to be the result of a damaged drainage pipe leading from a Containment Level 4 laboratory [1].

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or refer https://astell.com/news/media/battling-biohazardous-liquid-laboratory-waste