diff --git a/bw2io/extractors/ecospold2.py b/bw2io/extractors/ecospold2.py
index 95f3777..7639a6e 100644
--- a/bw2io/extractors/ecospold2.py
+++ b/bw2io/extractors/ecospold2.py
@@ -586,6 +586,8 @@ def extract_exchange(cls, exc):
             data["chemical formula"] = exc.get("formula")
         if exc.get("mathematicalRelation"):
             data["formula"] = exc.get("mathematicalRelation")
-
+        if exc.get("casNumber"):
+            data["CAS number"] = exc.get("casNumber").lstrip("0")
+        
         data.update(cls.extract_uncertainty_dict(exc))
         return data