Simplexml显示警告

我正试图从字符串中读取一个xml，但它显示了一些警告。我在xml字符串中找不到^，这是我正在使用的代码：

//$XMLstring=str_replace($XMLstring,'^','');
    $XML=simplexml_load_string($XMLstring);
    print_r($XMLstring);

这一条显示了警告，但也写入了$XMLstring。如果我取消注释第一行，则没有警告，但也没有打印。

编辑：我试图替换&使用str_replace的&，但现在它显示这样的警告：

Warning: simplexml_load_string(): Entity: line 1: parser error : 
Start tag expected, '<' not found in C:'xampp'htdocs'project'file1.php on line 173
Warning: simplexml_load_string(): &amp; in C:'xampp'htdocs'project'file1.php on line 173
Warning: simplexml_load_string(): ^ in C:'xampp'htdocs'project'file1.php on line 173

Warning: simplexml_load_string(): Entity: line 4: parser error : 
EntityRef: expecting ';' in C:'xampp'htdocs'project'file1.php on line 173
Warning: simplexml_load_string(): <item><col1>S&P 500</col1><col2>1656,96</col2>
<col3>0,86</col3><col4>14,16 in C:'xampp'htdocs'project'file1.php on line 173
Warning: simplexml_load_string(): ^ in C:'xampp'htdocs'project'file1.php on line 173
Warning: simplexml_load_string(): Entity: line 17: parser error : EntityRef: 
expecting ';' in C:'xampp'htdocs'project'file1.php on line 173
Warning: simplexml_load_string(): <item><col1>S&P/ASX 200</col1><col2>5123,36</col2>
<col3>0,94</col3><col4>4 in C:'xampp'htdocs'project'file1.php on line 173

下面是xml的示例：

<!--?xml version="1.0" encoding="UTF-8"?-->
<list>
  <item>
    <col1>S&P 500</col1>
    <col2>1656,96</col2>
    <col3>0,86</col3>
    <col4>66,19</col4>
</item>
</list>