Demonstrating contrast uptake by plants
The contrast agent gadolinium, which is used in medicine for magnetic resonance imaging (MRI), may enter the food chain through surface water. This is the result of an investigation by the BAM Federal Institute for Materials Research and Testing. BAM scientists irrigated cress plants over several days with water containing a contrast agent and then detected the contrast agent in the leaves.
Gadolinium is a toxic metal that can accumulate in the liver, spleen or bone. When it is injected into the bloodstream as a contrast agent in MRI, it is packaged in a chemical carrier. The compound is used to map different tissues by greatly increasing the contrast and is then rapidly secreted by patients without any major side effects. For several years, it has been assumed that the taking of gadolinium-based contrast agents might lead to an abnormal proliferation of conjunctive tissue in rare cases. Doctors call this disease Nephrogenic Systemic Fibrosis (NSF). The disease occurs mainly in patients with renal damage; in chronic kidney disease, they often suffer from iron deficiency. By ingesting iron-containing preparations, there is a kind of competition between the metals, the consequence being a degradation of the gadolinium complex and the release of toxic gadolinium into the body.
The contrast agent also passes into surface waters via sewage treatment plants and sewage since treatment plants can only filter out about ten percent of the agent, the scientists report in the "GIT Laboratory Journal"*. Thus, the gadolinium compounds may enter rivers and lakes and then ultimately the groundwater.
About 100 MRI scans are performed per 1000 inhabitants in Germany every year and the trend is rising. "It is estimated that 1100 kg of gadolinium complexes can be released via sewage each year into the environment in Germany," says Norbert Jakubowski of BAM. However, it remains unclear whether it can also get into the food chain through the water. The BAM scientists using cress have now shown how this works: "The contrast agent is absorbed through the plant's root system and accumulates there unchanged", said Jakubowski.
The studies show how easily contrast agents can enter the food chain. There are a number of contrast agents on the market whose chemical structure is different, but they always contain a gadolinium ion as a central core. The sensitive analysis methods used at BAM also allow a distinction to be made between these different contrast agent complexes. "The concentration found in the leaves corresponded to the concentration in the irrigation water", says Norbert Jakubowski. The scientists had irrigated the plants with water containing different gadolinium contrast agents. "In the plant extracts we were able to detect all of the contrast agents used", says Jakubowski. Still very little is known about pathways, degradation and accumulation of a contrast agent in the environment. "We see a need here for more research", says Jakubowski.