Design Entities with union architecture concepts

according concepts of Union Architecture, my entities(POCO) exist in inner layer, and it didn't any dependency to another project or libraries.

I'm using ArangoDB NoSql for my Data Access Layer, and I have to Use "ArangoDB Attribute" on my c# properties for mapping my properties to ArangoDD fields:

for example:

public class User
{
    [AliasField("_key")]
    public string Id { get; set; }
}

for this issue, I have to reference to Arango.Client Dll!:

Now, what I must be do for this problem? how can I remove my dependency?

any one can help me?