* STB Asset sells all TEPCO shares held by 4 SRI funds
* TEPCO shares had made up about 1.9 pct of firm's socially responsible investment funds
* STB Asset as whole managed 1.5 trillon yen as of March 2010 (Adds detail, comment)
TOKYO, April 5 (Reuters) - An asset management arm of Japan's Sumitomo Mitsui Trust Holdings said it had sold all shares in troubled Tokyo Electric Power held by four environmentally-responsible funds in the wake of a crisis at the utility's tsunami-hit nuclear plant.
STB Asset Management said it had about 1.9 percent, or around 500 million yen ($5.9 million), of the 26.5 billion yen ($315 million) worth of funds managed by the four so-called socially responsible investment funds in Tokyo Electric shares as of March 11 -- the day the plant was hit by a massive earthquake and tsunami.
The SRI funds had no exposure to Tokyo Electric shares by March 31, when total assets under management in the four funds stood at 24.8 billion yen.
STB Asset Management said it had removed the shares from the mutual funds as the unfolding crisis at TEPCO's Fukushima Daiichi nuclear power plant was causing serious environmental problems.
"Considering the nature of the SRI mutual fund, we decided to remove TEPCO shares from the portfolio," said an official at STB Asset.
He declined to comment on what managers of the firm's other active equity funds would do with any TEPCO shares they might hold.
STB Asset as a whole had 1.5 trillion yen of assets under management as of March 2010.
Shares of Tokyo Electric tumbled as much as 18 percent to a record low on Tuesday due to mounting investor concerns about the financial burden of dealing with the tsunami-hit nuclear reactors.
Tokyo Electric shares, fell by the daily 80-yen limit to 362 yen on Tuesday, down 18 percent and lower than the previous lifetime low of 393 yen hit in December 1951, according to Thomson Reuters data.
They have plunged 83 percent from their close of 2,121 yen on March 11.
($1 = 84.040 Japanese Yen) (Reporting by Michiko Iwasaki and Chikafumi Hodo; Editing by Nathan Layne and Joseph Radford)