Moody's Investors Service has placed certificates issued by a subsidiary of the China Ocean Shipping (Group) Co (Cosco) under review for a possible downgrade, citing a deteriorating operating environment for the shipping industry. The international -rating agency said the action was prompted by the weakening financial strength of Cosco - the mainland's biggest shipping company. In July last year, Cosco's United States arm privately sold US$300 million in bonds through its Cosco (Cayman) Freight Management Masters Trust in two tranches, backed by projected US dollar revenues from North American sea routes. The two series of certificates at present hold a Baa2 rating. Moody's Hong Kong office has not assigned any rating to Cosco (Hong Kong).