They've become as ubiquitous on British high streets as coffee shops – bubble tea outlets offering their Instagram-worthy drinks in countless flavour combinations.

The Taiwanese beverage, a blend of black tea, milk, sugar and chewy tapioca pearls, has gained global popularity since its origins in the 1980s. But recent findings suggest this trendy drink may warrant closer scrutiny.

A Consumer Reports investigation revealed high lead levels in some bubble tea products in the US, echoing previous concerns about cassava-based foods . (No equivalent UK testing has been published.)

The tapioca pearls – those signature "bubbles" – are made from cassava starch, and the root vegetable readily absorbs lead and other heavy metals from soil as it grows.

The tapioca pearls also pose other r

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