Land application of sewage sludge: scientific perspectives of heavy metal loading limits in Europe and the United States

Abstract

Heavy metals in sewage sludges accumulate in soils after successive sludge applications and can be toxic to plants, soil organisms, as well as humans and animals along the food chain. Because of this potential threat, many countries have set limits to the additions of metals in sludges to agricultural land, based on (i) the concentrations of metals in sludge itself, (ii) the loading, or total amount, of metal that can be added and often how quickly this can be applied, and (iii) the maximum concentrations of metals in soil which are allowed to build up after sludge applications. This review, based on regulations in the United States and some west European countries, shows that at present three basic approaches to setting limits can be distinguished: (i) a comprehensive analysis of the pathways of pollutant transfer to selected target organisms and an assessment of the likely harmful effects that metals may have on the target; (ii) setting limits consistent with the lowest observed adverse effect concentrations, which are actual cases of effects due to metals, but not necessarily derived from studies that involved land application of sewage sludge; and (iii) attempting to match the metal inputs to soil to the small losses of metals due to crop removal, soil erosion, and leaching ("metal balance approach"). These approaches are shown to result in widely different numerical limits being set for the same constituent, which is creating unease among the regulatory authorities worldwide. These differences appear to arise from at least two main sources. The first is whether, by a policy decision, zero impact is desired. This leads to very low limits, and is the philosophy behind the metal balance approach. The second is that those approaches that allow some increase in metal concentrations in soils often adopt different target organisms and these models suffer from the limited supply of relevant toxicity data, particularly information obtained from metals applied in sewage sludge. Differences in the philosophy behind environmental protection and in the choices of which organisms to protect explain the different metal limits for sewage sludge which have been adopted in the countries examined.Key words: zinc, cadmium, copper, chromium, nickel, lead, mercury, soil microbes, ecotoxicology, soil protection.

Synergistic effect of Chryseobacterium gleum sp. SUK with ACC deaminase activity in alleviation of salt stress and plant growth promotion in Triticum aestivum L.

“…FLI improved the polyphenol level which indicates the superior performance of isolate to decrease the salt stress. McGrath et al (1994) also reported that the inoculation of crops with organic waste accumulates the antioxidants. The presence of feather-degraded lysate in bioformulation is also contributed for increase in polyphenol content of wheat crops exposed to salinity (Fig.…”

Characterizing the solid–solution partitioning coefficient and plant uptake factor of As, Cd, and Pb in California croplands

“…Their accumulation in cropland soils poses a potentially serious threat to human and ecosystem health (de Meeus et al, 2002;Hinwood et al, 2004). To ensure that trace element levels in crops produced for human consumption do not cause unacceptable risks to the consumer health, regulatory authorities have established numerical limits for nonnutritive elements in fertilizers and other soil amendments based on outcomes of risk assessments (McGrath et al, 1994;Chen et al, 2007a).…”

Significance of soil copper in the urban development of horticultural soils

“…The fact that Cu tends to accumulate in the surface layers of many soils (McBride 1981 ;McGrath et al 1994) indicates that it is in stable forms which protect the Cu from being absorbed by plants or lost from the soil in drainage water.…”