How to retrive Image URL from Custom List,in sandbox solution using Visual studio(C#)

I'm trying to retrieve image/attachment url from custom list, while I am fetching image url and passing to img tag then it returns true rather Image URL,like src="true" and i want it like src="http://abc.png"

    private const string TitleColumn = "Title";        
    private const string Attchment = "Attachments";
    var webUrl = SPContext.Current.Web.Url;

    using (var site = new SPSite(webUrl))
    {
        using (var web = site.OpenWeb())
        {
            try
            {
                var List = web.Lists["SimpleList"];
                var spQuery = new SPQuery
                {
                    Query = "</Query><ViewFields><FieldRef Name=" + TitleColumn + "/><FieldRef Name=" + Attchment + "/>"
                };

                var Items = List.GetItems(spQuery);
                if (Items != null && Items.Count > 0)
                {
                    foreach (SPListItem item in Items)
                    { 
                        var ImageLink = new SPFieldUrlValue(item[Attchment].ToString());
                        imageTag.Attributes.Add("src", ImageLink.Url);                        
                        imageDiv.Controls.Add(imageTag);//image added to image div
                    }
                }
             }
            catch (Exception ex)  {   }                  
        }
    }

This approach works SSOM. How can I get the image url in sandbox solution SharePoint online CSOM?