The Director of Finance shall cause all moneys in the fund which are in excess of current requirements to be invested and reinvested from time to time in securities described in Section 16430 of the Government Code, and such securities may be sold or exchanged if in his opinion such sale or exchange is in the best interests of the state in effectuating the purposes of this chapter. All income derived from such investment, reinvestment, sale, or exchange shall be credited to the fund.