Basic

Sand, a key ingredient in concrete, has helped fuel construction booms and land reclamation around the world. But careless and sometimes illicit sand extraction has destabilised bridges and roads, wrecked ecosystems and stolen riverbanks and coastlines. It has led to water shortages and salt-water intrusion into farmer fields, killing crops. Those who work in the sand-mining industry often find themselves in precarious, exploitive and dangerous jobs. Melissa Marschke from the University of Ottawa and her colleagues write about the crisis fuelled by urbanisation and our seemingly boundless appetite for sand.

If you’re confused about whether or not to wear a face mask to stop the spread of coronavirus, you’re not alone. While countries such as France are mandating their use in certain circumstances, the UK and the WHO are sticking by their guidance that masks are not necessary for healthy members of the public. This leaves many of us wondering who’s got it right. The truth is, there isn’t sufficient evidence either way to guide governments on mask policy, which leaves them relying on one of two public health principles to decide what to recommend, explains Claire Horwell and Fiona McDonald.