Estimation of Zn and Cu unit output loads from animal husbandry facilities

Zinc (Zn) and copper (Cu) are toxic to aquatic organisms at very low concentrations that do not affect humans. We measured the daily output of Zn and Cu in wastewater from livestock farms to aquatic environments because waste from animal husbandryoperations contains high levels of Zn and Cu. At most pig farmsin Japan, a mixture of urine, some faeces, and service water is treated in onsite wastewater treatment facilities and discharged into a water body. Some dairy farmsalso have wastewater treatment facilities. We surveyed 21 pig farmsand six dairy farms. The unit (i.e., per head) output load from piggery wastewater treatment facilities ranged from 0.13 to 17.8 mg/head/d for Zn and from 0.15 to 9.4 mg/head/d for Cu. Over 70% of pig farmshad unit output loads of Zn and Cu below 6 and 2 mg/head/d, respectively. For dairy farms, the unit output load from wastewater treatment facilities was estimated at 1.8–3.6 mg/head/d for Zn and 0.6 mg/head/d for Cu. The unit output load for Zn from piggery wastewater treatment facilities was similar to that from treatment facilities for human waste. However, pig farmsgenerally raise several thousand to tens of thousands of pigs; pig farmsare therefore presumed to be a significant point source of Zn in rural areas.