Kerr McGee Posts a Drop in Profit  NEW YORK (Reuters) - Oil and gas producer Kerr-McGee Corp.  &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=KMG.N target=/stocks/quickinfo/fullquote"&gt;KMG.N&lt;/A&gt; on Wednesday reported a fall in quarterly profit,  citing a writedown related to a pigment plant and higher  environmental charges.