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Are There Heavy Metals In Colorado's Biosolids? <br />Colorado biosolids-and most biosolids-contain trace amounts of <br />metals. Biosolids may be recycled only when metal concentration levels <br />are suitable for application to farm lands, reclamation sites, or home and <br />garden use. Many of these metals-copper and zinc are two ex- <br />amples-are micronutrients required for plant and animal growth and <br />health. Domestic wastewater treatment plants cannot recycle biosolids <br />that exceed the metals limits. The table below shows those limits and <br />the average metals content for Colorado. <br />Colorado Department of Public Health & Environment <br />Maximum Metals Concentration (mg/kg, dry weight basis) <br />Metal Average Concentration* Limit for <br />in Biosolids Beneficial Use <br />Arsenic 7 75 <br />Cadmium 7 85 <br />Copper 636 4,300 <br />Lead 106 840 <br />Mercury 18 57 <br />Nickel 42 420 <br />• Selenium 10 100 <br />Zinc 750 7500 <br />*For the state of Colorado <br />How Do You Know <br />How Much Biosolids <br />To Use? <br />In agriculture, the <br />amount of biosolids used is <br />based on soil test results and <br />the estimated nutrients <br />needed for the crop to be <br />grown. The controlling factor <br />in Colorado is usually the <br />nitrogen that is taken up and <br />used for plant growth. Using <br />only the amount of nitrogen <br />needed for crop growth <br />• ensures optimum uptake of <br />nitrogen and prevents its <br />Alille'il /V a goOtl biosolids c/ op.