Perhaps you should try some spelling variations:
"pollution mexico-estado unidos-canada" » "collection mexico-estado unidos-canada", "pollution policy-estado unidos-canada", "pollution marine-estado unidos-canada"
"comercio mexico-estados unidos:el-canada" » "commerce mexico-estados unidos:el-canada", "commercio antico-estados unidos:el-canada"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("comercio mexico-estados unidos:el-canada") OR ("pollution mexico-estado unidos-canada")).
• Removing quotes may allow a broader search: (( comercio mexico-estados unidos:el-canada ) or ( pollution mexico-estado unidos-canada )).
• Adding a wildcard symbol may retrieve word variants: (("comercio mexico-estados unidos:el-canada") or ("pollution mexico-estado unidos-canada"))*.