Virtual currencies are retreating so broadly and sharply, it’s testing the durability of the cryptocurrency boom. The value of more than 7,000 tokens tracked by CoinGecko has shrunk more than $600 billion in the past week to $1.9 trillion. Bitcoin, the largest cryptocurrency, slid some 11 per cent Wednesday to break below $40,000 and is now about $25,000 off its record high set in April. Multiple factors are at play, ranging from criticism of the environmental impact of Bitcoin’s energy usage by onetime proponent Elon Musk, to the risk of a regulatory squeeze on what some have called the Wild West of investing. Digital tokens have also delivered gains so fat that some traders may have been taking profits.