High levels of a toxic chemical have been detected in Glasgow waterway, turning the burn bright green, are to be flushed into the River Clyde.

Officers from the Scottish Environment Protection Agency (SEPA) have sealed off the Polmadie burn, which runs through Richmond Park in the south of the city, after tests revealed high concentrations of hexavalent chromium in the water.

Local residents had raised the alarm after noticing the water had become "luminous green" in late January.

Decontamination has been ongoing in the area for years to rid it of potentially hazardous industrial chromium left behind in the ground by the former J&J White's Chemical Works, which closed in 1967.

Exposure to hexavalent chromium is known increase the risk of lung cancer, asthma, kidney and liver problems and irritates skin and eyes.

Temporary 'Heras' metal fencing has now been erected around the burn following warnings from environmental health officers that the site posed a potential risk to public health.

The J&J White's Chemical Works operated in Rutherglen from 1820 until 1967. Much of the waste by-products in form of Chromite Ore Processing Residue were used to back fill the former clay pits, near the West Burn in Shawfield, resulting in a legacy of contamination.

Investigations established that the Polmadie Burn was becoming contaminated with chromium flowing into it from the nearby West Burn Culvert Diversion, which is routed underground and passes through the site of some of these former backfilled clay pits.

To deal with the problem, a decision was taken and work carried out on 21 January to divert the culverted West Burn. The diversion redirected a significant proportion of the contaminated water which used to flow into the Polmadie Burn away, carrying it straight into the River Clyde instead where it is diluted enough not to pose a public health risk.

However, SEPA believe that the current contamination of the Polmadie Burn has occurred because the time of the West Burn diversion coincided with a dry period, meaning the residual water which flowed into the Polmadie Burn had higher than normal concentrations of chromium in it.

In addition, groundwater from the abandoned culvert also continues to leak into the Polmadie Burn until the culvert is fully sealed up, which is expected to take another two weeks to complete.

A proposal to allow more water to flow into the Polmadie Burn to dilute the chemicals has been agreed following a meeting between Glasgow City Council, SEPA and Clyde Gateway. The flushing process requires a licence from SEPA and must be done in a controlled manner. The water will eventually flow into the River Clyde.

A spokeswoman for Glasgow City Council said: “Following a site visit last week and confirmation about the temporary high concentration of hexavalent chromium in the Polmadie Burn, Heras fencing has been put in place to restrict public access and there is an agreed proposal to temporarily increase the flow of the burn, in a controlled way, to dilute the level of chromium.”

"[SEPA] expect that the majority of the chromium that used to get into the Polmadie Burn has now stopped, but until the abandoned West Burn culvert is fully sealed, some contamination from the groundwater may continue to get there, but in much smaller volumes than before.

"The reduced dilution in the Polmadie Burn is making the contamination look more concentrated, so for now it looks worse (greener). Once the abandoned culvert is fully sealed, and is no longer acting as a pathway, SEPA expect to see the colour gradually disappear and that heavy rainfall would speed this up considerably."

What is hexavalent chromium?

Hexavelent chromium is a heavy metal with a number of uses across industries including textile dyes, paints and plastics.

While metallic chromium is inert and safe, in certain chemical compounds chromium forms ions with a plus-six positive charge. If this hexavalent form of chromium then gets into the body – eaten, or dissolved in water, or vaporised by a welding torch and then inhaled – it can cause cancer.

It was restricted from use in electronics manufacturing in EU countries in 2003 under the Restriction of Hazardous Substances Directive.

It was listed alongside nine other elements including lead and mercury.