The Dow Jones Industrial Average ended Monday trade at session lows, starting the week on a downbeat note, eroding what had been a solid gain for April, as declines in health-care, industrials and materials undercut upbeat buying sentiment on the back of a series of merger announcements. The Dow closed down about 150 points, or 0.6%, at 24,163, the S&P 500 index finished down 0.8% at 2,648, with the health-care sector notching a 1.6% decline and industrials and materials both falling by at least 1.3% on the day. The technology-laden Nasdaq Composite Index finished the day off 0.8% at 7,066. For the month, the Dow and S&P 500 closed with a monthly rise of 0.3%, while the Nasdaq rose less than 0.1% for the month. The market's had opened firmly higher after Sprint Corp. fell and wireless carrier T-Mobile US Inc. announced an all-cash bid on Sunday, valuing Sprint at about $26 billion.