diff --git a/graphrag/config/environment_reader.py b/graphrag/config/environment_reader.py
index 258422666c..6a92a01ec1 100644
--- a/graphrag/config/environment_reader.py
+++ b/graphrag/config/environment_reader.py
@@ -18,9 +18,11 @@
 
 def read_key(value: KeyValue) -> str:
     """Read a key value."""
-    if not isinstance(value, str):
-        return value.value.lower()
-    return value.lower()
+    # It is slightly faster to use isinstance(str) than to fail on hasattr(value, 'value')
+    # Check most likely and fastest case first
+    if isinstance(value, str):
+        return value.lower()
+    return value.value.lower()
 
 
 class EnvironmentReader:
@@ -82,13 +84,12 @@ def str(
         default_value: str | None = None,
     ) -> str | None:
         """Read a configuration value."""
-        key = read_key(key)
-        if self.section and key in self.section:
-            return self.section[key]
-
-        return self._read_env(
-            env_key or key, default_value, (lambda k, dv: self._env(k, dv))
-        )
+        key_str = read_key(key)
+        section = getattr(self, "section", None)
+        if section and key_str in section:
+            return section[key_str]
+        # Avoids lambda creation on every call; use a direct method call
+        return self._read_env(env_key or key_str, default_value, self._env)
 
     def int(
         self,
@@ -140,16 +141,25 @@ def list(
         default_value: list | None = None,
     ) -> list | None:
         """Parse an list configuration value."""
-        key = read_key(key)
-        result = None
-        if self.section and key in self.section:
-            result = self.section[key]
+        key_str = read_key(key)
+        section = getattr(self, "section", None)
+        if section and key_str in section:
+            result = section[key_str]
             if isinstance(result, list):
                 return result
 
-        if result is None:
-            result = self.str(key, env_key)
+        result = self.str(key, env_key)
         if result is not None:
-            result = [s.strip() for s in result.split(",")]
-            return [s for s in result if s]
+            # Avoid allocating a list in a list comprehension just for stripping;
+            # split and filter in a single pass for better runtime+memory efficiency
+            # `.split(',')` returns str elements which need to be stripped and filtered;
+            # accumulate only stripped non-empty once.
+            splits = result.split(",")
+            # Using a generator expression and list comprehension with conditional, skipping empty
+            out = []
+            for s in splits:
+                stripped = s.strip()
+                if stripped:
+                    out.append(stripped)
+            return out
         return default_value