Jens Chr. Tjell

Atmospheric lead pollution of grass grown in a background area in Denmark.

LEAD in the atmosphere of the Northern Hemisphere originates mostly from lead-alkyl petrol additives emitted from car exhausts1. A small proportion of this lead—estimated at about 10%2,3—is deposited within 50–100 m of the road while the rest is presumably transported long distances before deposition. There are reports of increasing concentrations of lead in roadside vegetation with decreasing distance from the edge of the road1,4,5. This apparent lead contamination ceases beyond 100–200 m from the road, and it is said therefore that airborne lead is not a significant source of lead in crops in general5–7, although there is circumstantial evidence to the contrary8,9. We report here, however, that the lead taken up by grass in a remote rural area is predominantly from the atmosphere.

Plant uptake of airborne cadmium

Abstract Atmospheric inputs of cadmium directly to a selection of agricultural crops, via surface contamination, were determined in Eastern Denmark by isotopic labelling of the experimental soils. Bulk precipitation of cadmium in the growth period was measured in the range 12–26 μg m−2 (30 day)−1. The cadmium concentrations in the experimental plants were in the range 0·08–0·79 μg g−1. These figures confirm that the experimental site was situated in an unpolluted agricultural area not influenced by local emissions of the metal. Atmospheric cadmium surface contamination of crops contributed 0·02–0·4 μg g−1 to the dry matter, or 20–60% of the total plant cadmium. The atmospheric cadmium appears to be absorbed into, and transported throughout the volume of the plant. Airborne cadmium thus seems to be a significant contribution to the cadmium content in crops and thereby to the human food intake of this toxic metal.

Plant uptake of airborne mercury in background areas

Atmospheric input of mercury directly to selected crops was determined in Eastern Denmark by isotopic labelling of experimentel soils. Bulk precipitation in the growth period corresponds to 200 ng·m−2·d and the mercury concentrations in the experimental plants were in the range of 5 – 20 ng·g−1 (wet weight). These figures indicate that the experimental site was situated in an unpolluted agricultural area not influenced by local emissions of the metal. Atmospheric mercury contamination of the crops contributed more than 90% of the total plant mercury in the green parts. The atmospheric mercury appeared to be absorbed into and transported throughout the whole plant. Even in the subterranean part of a plant the atmospheric contribution was approximately 50%. Airborne mercury thus seems to contribute significantly to the mercury content in crops and thereby to the human food intake of this toxic metal.

Atmospheric lead input to agricultural crops in Denmark

Abstract The plant uptake of lead from soil is reported for several edible crop species under field conditions using an isotopic dilution method. The species investigated acquire from soil 0.02–0.08 mg Pb/kg (dry matter). It is concluded that the remainder originates from the atmosphere. From the uptake determinations it is estimated that the soil supplies directly and indirectly only around 0.02 mg Pb/day per person in Denmark; the difference up to the daily intake (0.08 mg Pb/day per person) must come from the atmosphere, or other sources of contamination.

Leaching from land disposed municipal compost: 4. Heavy metals

The leachates from 17 lysimeters containing composts of varying origin, age (3 and 12 months), and packing depths (15–50 cm) were monitored for a 2.5-year period. This paper reports on the results on heavy metals. The initial leachate concentrations exceeded the drinking water standards for all heavy metals studied (Cd, Ni, Co, Zn, Cu, Pb, Cr), but after one and half year of leaching (c.450 mm leachate) only Ni exceeded the standard. Ni was identified as the most serious heavy metal pollutant but was considered less critical than nitrogen compounds and organic matter previously reported in the leachate. The heavy metal leaching is only moderately affected by compost origin, compost age and packing depth. The first year of leaching released between 0.1% (Pb, Cr) and 1.9% (Ni) of the original compost heavy metal content.

Prediction of Cadmium Concentrations in Danish Soils

Detailed studies on the effects of sludge utilization in agriculture have been conducted in Denmark since 1973.

Cadmium in soil and terrestrial biota, with emphasis on the danish situation

The cadmium load on the soil and terrestrial biota in the industrialized countries appears to be on the increase. Due to a relatively high mobility of this metal in the soil-plant system, the likely gradual increase in soil concentrations will influence the cadmium load on organisms in the terrestrial biota. It might be too early to predict the actual rate of increase in the cadmium load on specific organisms but some attempts to do so have suggested an annual increase rate of 0.5-2% in the human food intake of the metal. Although the present cadmium pollution of the environment at large is not yet crucial, the most sensitive species, man and other long-lived mammals, might soon need introduction of countermeasures to seriously reduce the load of this toxic metal. The most feasible countermeasures to be taken are reductions in emission to air directly or indirectly via reduction of the indiscriminate use of the metal for common consumer goods. A decrease of the inflow to soils in phosphate fertilizer may be more difficult to curb, but a reduced fertilization rate on most areas might be possible without loss of fertility. Sludge may not be a major source of cadmium nationally, but may locally significantly increase the inflows to agriculture (Statens Naturvårdsverk, 1978; Miljøstyrelsen, 1980; Umweltbundesamt, 1981; Department of the Environment, 1980.

Phosphorus recovery from sewage for agriculture

Abstract Land application of sewage sludge seems justifiable mostly because of its phosphorus content. Depending on the distribution of cattle manure the total Danish supply of phosphorus could be provided by manure and sludge. Or sludge phosphorus could substitute from 30–100% of all imported raw phosphates utilized domestically for agricultural purposes. Increased sludge phosphorus production would require extended waste water treatment. Due to increased costs of imported phosphorus such treatment may actually prove economically sound using well known technology. Furthermore it may reduce eutrofication of receiving waters. Recent research shows that Danish sludge need not contribute more Cadmium to soil than chemical fertilizers, if both are applied only accordingly to plant phosphorus demand. Consequently, increased sewage sludge application in agriculture should be deemed favourable compared with present extensive use of chemical fertilizers.

The Degradation of Specific Organic Compounds with Landfill Leachate as a Primary Substrate

The biodegradation of 22 specific organics have been investigated in the presence of sanitary landfill leachate and under aerobic and denitrifying conditions. All compounds except chlorinated alifatics were degraded under aerobic conditions. Chlorinated compounds, nitrobenzene and o-nitrophenol were generally more resistant to degradation. Aromatics with two- or more rings, phenol and 2-hydroxy-toluene were degraded very fast. Under denitrifying conditions only nitrobenzene and tetrachloromethane were degraded.

Phosphorus Agriculture Sewage for Agriculture

Land application of sewage sludge seems justifiable mostly because of its phosphorus content. Depending on the distribution of cattle manure the total Danish supply of phosphorus could be provided by manure and sludge. Or sludge phosphorus could substitute from 30—100% of all imported raw phosphates utilized domestically for agricultural purposes. Increased sludge phosphorus production would require extended waste water treatment. Due to increased costs of imported phosphorus such treatment may actually prove economically sound using well known technology. Furthermore it may reduce eutrofication of receiving waters. Recent research shows that Danish sludge need not contribute more Cadmium to soil than chemical fertilizers, if both are applied only accordingly to plant phosphorus demand. Consequently, increased sewage sludge application in agriculture should be deemed favourable compared with present extensive use of chemical fertilizers.