ColisorTigela.cs

using UnityEngine;
using System.Collections;

public class ColisorTigela : MonoBehaviour {

    // Use this for initialization
    void Start ()
    {

    }

    // Update is called once per frame
    void Update ()
    {
        if (gameObject.transform.position.z < Camera.main.transform.position.z)
        {
            DestroyThis();
        }
    }

    void OnCollisionEnter(Collision collision)
    {
        DestroyThis();
    }

    void DestroyThis()
    {
        Destroy (gameObject);
        Destroy (this);
    }
}