What is the relationship between 'smelting' and 'metal' in the context of the input sentence.
Options: publisher, distributed by, product/material produced, director/manager

Keller Rohrback has also handled environmental litigation involving home heating oil, contaminated drinking water, contaminated sediments, landfill leachate, metal smelting and finishing wastes, tank farms, chemical plants, gas stations, and major manufacturing concerns.
product/material produced