GroCo safety and qualityGroCo compost is regulated under the Washington State Department of Ecology biosolids program. Each batch of GroCo compost is laboratory tested to ensure it meets quality standards for trace metals and pathogen reduction. GroCo meets these standards, earning the rating of Exceptional Quality (EQ) biosolids product. What about trace metals?The concentration of trace metals in GroCo is well below state standards set for biosolids products (see biosolids content analysis). The Department of Ecology also sets limits for composts made from other organic residuals. GroCo also meets the limits for these other composts:
| Trace Metals | GroCo | Washington State
compost quality
trace metal limits |
|---|
| Parts per million (ppm) |
| Arsenic |
0.26 |
20 |
|---|
| Cadmium |
0.79 |
10 |
|---|
| Copper |
143 |
750 |
|---|
| Lead |
20 |
150 |
|---|
| Mercury |
1.0 |
8 |
|---|
| Molybdenum |
2.3 |
9 |
|---|
| Nickel |
11 |
210 |
|---|
| Selenium |
100 |
18 |
|---|
| Zinc |
169 |
1400 |
|---|
What about pathogens?GroCo is tested for disease-causing micro-organisms such as bacteria, viruses and parasites. Biosolids treatment kills more than 90% of such organisms and the composting process destroys any that may remain. Laboratory results confirm that pathogenic organisms are not present in GroCo and meets the designation of Exceptional Quality. Ensuring compost quality Compost producers work to ensure that their products meet the high quality demanded by their customers. For example, in 2002, damage to landscape and garden plants was traced to an herbicide, clopyralid, which had been found in several Washington composts. In response, many composts and ingredients were tested to ensure that sources of contamination were identified. Sources included use of chlopyralid in landscaping, lawns and in weed-free hay and straw grown for livestock use. Although we did not expect that biosolids or sawdust would contain clopyralid, samples of GroCo compost were laboratory tested and found to contain no clopyralid. GroCo was also tested in plant bioassays conducted by Washington State University and University of Washington, where plants showed no indications of clopyralid damage.
The Washington State Department of Agriculture subsequently banned use of chlopyralid on residential lawns in order to protect compost quality. Other beneficial uses of King County biosolids: |
