Epsilon Archive for Student Projects

Abstract

The level of cadmium (Cd) in Swedish arable land has increased during the last century and the average concentration of Cd in the plough layer is today 0.23 mg/kg. The increase is mainly due to anthropogenic activities such as phosphorus fertilizing, liming, import of feed, and atmospheric deposition from industrial emissions. Cadmium in the soil will be taken up by crops and is thereby transferred to humans via food. Carrot is one of the crops of concern, both because it may contain quite high Cd concentrations and due to the large consumption in Sweden.

In the body, Cd is stored mainly in the liver and the kidneys and may cause several diseases already at low concentrations. Due to these findings, the recommendation for Cd intake has recently been lowered and should not exceed 2.5 µg per kg body weight/ week. This means 25 µg per day for a person weighing 70 kg. To decrease the Cd uptake by plants liming is often recommended, however the results of liming are inconsistent. When adding lime several soil factors, such as pH, Ca concentration, and ion strength is altered which may affect the Cd availability and uptake by plants.

The aim of this Master thesis was to study the effects of liming and Ca2+ on the Cd uptake by carrots. In order to do that, two experiments were conducted. The long-term experiment was conducted in a climate chamber where the carrots were grown in a sand/peat substrate for eleven weeks. Two levels of Cd were tested, 0.23 and 2.3 mg/kg soil, in combination with three pHs: 4.6, 5.6, and 6.6. The pH was altered by addition of lime. In the short-term experiments the Cd uptake by plants was tested in nutrient solutions. Two different pH levels were used, 5.6 and 6.6. Each pH was combined with three levels of Ca, 2.25, 4.5, and 9 mM.

The results from the long term experiment showed increased Cd uptake with increasing pH. However, since the concentrations of Cd and Ca follow each other in all treatments and were well correlated to the plant weights it seems like the Cd uptake was mostly affected by plant growth. Results from the short-term experiment showed decreased Cd uptake with increasing pH. The results also indicate that high Ca concentrations may lower the Cd uptake. However the effect of Ca seems only to be valid at low pH.