An Italian tanker carrying 6,000 tons of toxic chemicals sank this week in the English Channel not far from the French coast after being abandoned by its crew during a storm, and it has begun leaking highly toxic styrene. The tanker, which was carrying chemicals for Shell and ExxonMobil, was the second to sink off the coast of France within a year. The first caused a massive oil spill last December that polluted a good deal of the nation’s Atlantic coastline. The irate French are saying the second spill underscores the point they have been making about the need for stricter maritime safety rules. The Italian tanker would have been banned from European Union waters under tighter rules proposed by France after last year’s disaster.