(NEXSTAR) — The value of Bitcoin fell sharply Wednesday afternoon after Elon Musk announced in a tweet that Tesla would be suspending Bitcoin vehicle purchases over environmental concerns.

“We are concerned about rapidly increasing use of fossil fuels for Bitcoin mining and transactions, especially coal, which has the worst emissions of any fuel,” Musk tweeted just after 6 p.m. EST. “Cryptocurrency is a good idea on many levels and we believe it has a promising future, but this cannot come at great cost to the environment.”

Musk said that Tesla would hold the Bitcoin it owns to use “as soon as mining transitions to more sustainable energy.” Tesla bought $1.5 billion worth of Bitcoin in February, according to an SEC filing.

Cambridge researchers noted a spike in Bitcoin mining after the electric car company announced the purchase, estimating that the amount of electricity — already comparable to that used by countries like Argentina or the Netherlands, roughly 121.9 terawatt hours — had jumped to the usage level of Malaysia or Sweden, about 147.8 terawatt hours.

Musk said Wednesday that the company would still look into using more sustainable cryptocurrencies.

The price of Bitcoin fell 5% after the tweet:

Other company’s including Jack Dorsey’s Square and major Wall Street banks bought Bitcoin after the cryptocurrency’s value soared from $3,500 in February of 2019 to more than $63,000 in mid-April.