What is one of the biggest problems in cities around the world?

Yes that is one of the biggest problems city officials are facing. I hope scientists will come up with an invention that will finally solve this problem. The worse are industrial wastes, nuclear and toxic wastes that remain active for thousands of years. Proper recycling can help alleviate the situation but something must be done before it's too late.

well the bigest problem around the world is accomdation place to live,and ofcoure garbage is also a big problem.

Housing problem, temporary tinny of homeless peoples narrow road is big problems in big city.

social services never keep up with population growth and when population declines the increasing costs over come the budget