Influence of soil factors on the accumulation of cadmium by lettuce

Cadmium is one of the more mobile heavy metals in the soil-plant system. Its accumulation in plants is especially important from the point of view of its entering the nutrient chain. It is equally toxic for plant, animal and human organisms. Cadmium is easily taken up by plants and is among the biologically most accumulative heavy metals. We carried out pot experiments with different types of soils to examine how the different soil properties influenced cadmium up-take by plants. The Soil Conservation Information and Monitoring System (TIM) is part of the Environment Protection Information System, the starting point of an agricultural environment management program launched in Hungary. The TIM has 1200 measuring points. In accordance with the examination data, we picked some points where the pH value and the Cd content of the soils may justify the testing of Cd uptake by plants. It was near these points, at five test sites that we collected soil samples from a 0-20 cm deep surface layer for our experiments. We chose lettuce (Lactuca sativa L.) as test plant, as in our earlier experiments we had found that it was this plant that best accumulated Cd in its leaves thus we thought it might prove a good marker/indicator on soils with lower Cd contents. We tried to establish correlations between the total and available Cd content of soil, its pH value, clay content, organic matter content, hydrolytic acidity, cation adsorption capacity, and the Cd concentration and total uptake by lettuce. According to our experiment findings, clay, silt and organic matter content of the soils had no effect on Cd uptake. In lettuce leaves the Cd concentration was 1.4-16 times as much as the total Cd content of the soil. There was a negative linear correlation existing between the pH value of the soil and the Cd uptake by lettuce (r = -0.409, p<0.05). We also, found a close correlation between the Cd concentration of the lettuce leaves, its Cd uptake and the hydrolytic acidity of soils. Consequently the Cd uptake increases with increasing hydrolytic acidity.