Doubts cast on microplastic studies as experts float lab glove contamination theory

The amount of microplastics thought to be present in nature and human organs may have been exaggerated by a compound in scientists’ labratory gloves, a new study has claimed.

In recent years, alarming reports have emerged that microplastics, particles smaller than five millimetres, have been discovered in rivers, soil, Antarctic ice, blood, urine and breast milk.

One report also implied that human brains had been found to be contaminated with up to a teaspoon’s-worth of plastic.

However, scientists from the University of Michigan have raised the possibility that samples may have been contaminated by tiny compounds on laboratory gloves.

The study, which has been published by the Royal Society of Chemistry, shows that tiny residues from the gloves, known as stearate salts, can easily be mistaken for the microplastic polyethylene.

When a laboratory glove comes into contact with a surface, it can leave behind microscopic traces of stearate salts, with common laboratory tests such as infrared struggling to distinguish the difference.

Researchers use vibrational spectroscopy to identify microplastics, which entails measuring how the particle interacts with light to produce what scientists call a chemical fingerprint.

Because polyethylene and stearate salts have very similar structures, they also interact with light in a similar way.

Professor Anne McNeil and Madeline Clough, who carried out the research, wrote on The Conversation website: “Our team found that, even when following established protocols, using certain methods to measure environmental microplastics can potentially contaminate the results.”

They added: “As a result, much of this research may be overestimating the number of microplastics.”

They have both stressed however that the study does not mean that plastic pollution is not widespread and that microplastics are not harmless.

Small plastic particles are everywhere, and so exposure is inevitable.

While these findings do not dispute this fact, it points out that gloves have largely escaped suspicion and may be contributing to high percentage of microplastics discovered in objects.

An experiment found that simple contact with gloves produced “false positives” at a rate of 2,000 particles per square millimetre, meaning a surface can appear polluted with plastic when it has merely been handled.

Laboratories are becoming more aware of contamination risks, with multiple analytical techniques increasingly being used on the same samples to cross-check results.

The study notes that researchers will hopefully be able to develop standard operating procedures for analysing microplastics in human tissues and other biological samples.