The FTSE 250 index is down 2% as fears of a nuclear catastrophe in Japan continue to weigh down on sentiment.Falling oil prices have hit Heritage Oil which is down over 13%. Insurance underwriter Lancashire Holdings is also making losses after saying it is too early to give a meaningful estimate of costs relating to the loss of life and property damage following the earthquake and tsunami in Japan.Record average prices for stones from its Let?eng and Ellendale mines towards the end of 2010 helped diamond miner Gem lift profits by nearly 40% last year. Nevertheless, shares were down 4%.Also lower is infrastructure investment firm HSBC Infrastructure after upping its investment in the Dutch higher speed rail public/private partnership project.Among the risers are retailers Sports Direct, JD Sports and Home Retail Group.FTSE 250 - RisersHansen Transmissions International NV (DI) (HSN) 47.01p +6.24%RPS Group (RPS) 210.30p +5.63%JD Sports Fashion (JD.) 902.00p +1.75%Keller Group (KLR) 602.00p +1.18%Home Retail Group (HOME) 195.00p +1.14%Sports Direct International (SPD) 182.10p +1.11%Synergy Health (SYR) 816.50p +1.05%Rank Group (RNK) 131.30p +1.00%BBA Aviation (BBA) 202.10p +0.95%Dairy Crest Group (DCG) 360.30p +0.92%FTSE 250 - FallersHeritage Oil (HOIL) 287.40p -13.49%Renishaw (RSW) 1,557.00p -8.41%St James's Place (STJ) 307.30p -7.33%AZ Electronic Materials SA (WI) (AZEM) 255.70p -5.78%Exillon Energy (EXI) 415.00p -5.68%Hochschild Mining (HOC) 591.50p -5.06%Thomas Cook Group (TCG) 169.20p -5.05%ITE Group (ITE) 230.50p -4.99%Kenmare Resources (KMR) 35.10p -4.93%Centamin Egypt Ltd. (CEY) 125.50p -4.92%