COLUMBIA, S.C. (AP) _ Standard and Poor's has downgraded the ratings of Safety-Kleen Corp. and Laidlaw Inc. to D, or default, the lowest possible.

The bond rating company lowered the ratings Tuesday. Safety-Kleen's debt had carried a CC rating and Laidlaw, which owns a piece of the Columbia hazardous waste management and recycling company, had carried a BB- rating. All those grades are considered ``junk'' status.

On Monday, Safety-Kleen said it would not be able to make a $10.4 million interest payment due this week. The company said earlier it had an agreement with its creditors to wait until May 30 for the payment.

In March, Safety-Kleen began an internal investigation of its accounting practices and suspended its three top officers. Those officers resigned Friday.

The company, which has yet to report second-quarter earnings, has said the accounting irregularities would require it to restate earnings for the past three years.

Safety-Kleen shares closed at 75 cents each Wednesday, unchanged on the New York Stock Exchange.