Nitrogen and phosphorus compounds are important, as they arenutrients for organisms, e.g.algae, in recipients. As a result of the growth ofalgae, secondary processes can proceed in the recipient, forming furtherorganic substances which, when they decompose, can result inconsiderably higher oxygen demand than is caused by primary organicpollutants in the sewage effluent.Heavy metals may be toxic in high concentrations and may disturb theecosystems also in low concentrations.
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