Further retreating from record highs, Bitcoin slumped 10% on Thursday (January 21) to a 10-day low. The world's most popular cryptocurrency has lost nearly a quarter since touching a record $42,000 on January 8th. The pullback comes amid growing concerns that bitcoin is one of a number of financial market price bubbles. Traders also said that fears U.S. President Joe Biden's administration could attempt to regulate cryptocurrencies have weighed on sentiment. During a Senate hearing on Tuesday (January 19) Janet Yellen, Biden's pick to head the U.S. Treasury, expressed concerns that cryptocurrencies could be used to finance illegal activities. She said: "I think we really need to examine ways in which we can curtail their use and make sure that money laundering does not occur through these channels". One cryptocurrency broker told Reuters that the comments had a substantial impact. Adding that it was still unclear exactly what, if any, moves the Biden administration would take.