Detection of a tiny amount of a potentially dangerous radioactive isotope on a Suffolk beach may be down to improved monitoring abilities, according to a year-long investigation by the Environment Agency.

The investigation has failed to conclusively pinpoint the source of the contamination but concludes that at the level the isotope was detected there is “negligible” risk to human health.

The isotope, known as Strontium-90, was detected in sand taken from the beach at Aldeburgh during monitoring in the autumn of 2015. Five local beaches are routinely monitored each year.

While Strontium-90 emits beta radiation, officials say the level found was tiny compared with the average amount of such radiation routinely found in a human body.

Strontium-90 can be produced by a nuclear reactor but can also be created by atomic fuel reprocessing, such as that carried out at Sellafield in Cumbria. Discharges from Sellafield have been found along many stretches of the UK coast.

Contamination of the sand at Aldeburgh could even be a residue from nuclear accidents elsewhere in the world or from nuclear weapons testing carried out more than half a century ago.

A possible link with Sizewell A has been investigated but the Environment Agency points out that radioactive discharges from the power station have declined sharply since it ceased electricity generation at the end of 2006.

The agency’s report explains that sampling methods have become more refined and, prior to the detection of the Strontium at Aldeburgh, a new laboratory had taken over the contract for analysis.

“It is therefore likely that the levels of Strontium in the sand have historically been around the limit of detection for the method used and the improvement in methodology combined with a change in the laboratory have resulted in greater likelihood of seeing this activity,” the report adds.

Magnox, which is managing Sizewell A on behalf of the Nuclear Decommissioning Authority, believes there are no safety or environmental concerns and no risk to members of the public.

EDF Energy, which owns and operates Sizewell B, has ruled out any connection because of the “signature” of the radioactive isotope concerned.