Fill DROPDOWNLIST with another DROPDOWNLIST asp.net razor

I need to populate a dropdownlist with another dropdownlist selection, but I do not know how to retrieve it when working with ICollection, below the classes below.

using System;
using System.Collections.Generic;

namespace TECNOSOL.Domain.Entities
{
    /// <summary>
    /// Resíduo
    /// </summary>
    public class Residuo
    {
        public int ResiduoID { get; set; }
        public string Nome { get; set; }
        public string ABNT { get; set; }
        public string CONAMA { get; set; }
        public string IBAMA { get; set; }
        public string TAGs { get; set; }

        // Densidade
        public Nullable<int> OperadorDensidadeID { get; set; }
        public Operador OperadorDensidade { get; set; }
        public Nullable<decimal> Densidade { get; set; }

        // Energia
        public Nullable<int> OperadorEnergiaID { get; set; }
        public Operador OperadorEnergia { get; set; }
        public Nullable<decimal> Energia { get; set; }

        // Tecnologias
        public virtual ICollection<ResiduoTecnologia> ListaTecnologia { get; set; }
    }
}

-

using System.Collections.Generic;

namespace TECNOSOL.Domain.Entities
{
    /// <summary>
    /// Tecnologia do Resíduo
    /// </summary>
    public class ResiduoTecnologia
    {
        public int ResiduoTecnologiaID { get; set; }
        public string Nome { get; set; }

        public virtual ICollection<Residuo> ListaResiduos { get; set; }
    }
}

I need that when selecting the waste, it only brings the waste technologies that are marked in the Collection, how to do it?