Admob Unity Plugin - Mute interstitial ads

Hey guys I am really hoping for some help on this one. In my game I have a button that once pressed mutes all sound and music. I have monetized my game with Google Admob and I am using the official Admob Unity Plugin. My problem is that when an interstitial is shown it is not muted. I want to mute my ads when my game is muted. Can anyone help me accomplish this?

My script for displaying ads looks like this:

 using UnityEngine;
 using System.Collections;
 using GoogleMobileAds.Api;
 
 public class AdmobScript : MonoBehaviour {
 
     private static string interstitialId;
     private static InterstitialAd interstitial;
     private static AdRequest interstitialRequest;
     public static int counter;
 
     void Awake()
     {
         DontDestroyOnLoad(gameObject);
     }
         
     void Start () 
     {
         #if UNITY_ANDROID
         interstitialId = "ca-app-pub-1518441074738585/3382052954";
         #elif UNITY_IPHONE
         interstitialId = "ca-app-pub-1518441074738585/2544448158";
         #else
         interstitialId = "unexpected platform";
         #endif
 
         counter = 0;
         requestInterstitial ();
     }
     
     public static void requestInterstitial()
     {
         interstitial = new InterstitialAd (interstitialId);
         interstitialRequest = new AdRequest.Builder ().TagForChildDirectedTreatment(true).Build ();
         interstitial.LoadAd (interstitialRequest);
     }
 
     public static void showInterstitial()
     {
         if (interstitial.IsLoaded()) 
         {
             interstitial.Show ();
         }
     }
 
     public static bool isAdReady()
     {
         return interstitial.IsLoaded ();
     }
 }