MORE AND more US companies are appointing executives for environmental affairs, according to a survey of Fortune 500 companies. Consultant Arthur D Little says 49 of the top 100 US companies on the Fortune 500 list appointed "green" executive vice-presidents in 1991, a rise from 38 the previous year. Another 31 companies, in 1991, named executives directly responsible for environmental affairs as against 25 in 1990.