Risk assessment of potentially toxic metals in soil and fertiliser products - fate and effects in the food chain and the environment in Norway

Due to insufficient data, it is uncertain how large a possible increase on the substances will be, and it is important to follow developments.

This is the key message in a risk assessment VKM has made on behalf of the Norwegian Food Safety Authority.

Arsenic, cadmium, chromium, copper, lead, more, nickel and zinc are found in the soil and as pollution in fertiliser products. When fertilizer products containing these substances are spread in soil over several years, they can accumulate and be stored in the soil. This can have a negative effect on the environment and for the health of animals and humans.

The technical term for this is "potentially toxic elements”.

Methods

VKM has assessed the consequences of using various fertiliser products containing potentially toxic elements. Fertiliser products included in the risk assessment are mineral fertilisers, manure from cattle, pigs, poultry, and horses, biowaste based on food waste, and a mixture of manure and food waste and fish sludge.

VKM has assessed the current limits in the quality class II fertiliser products regulations and compared these to test results for the various fertiliser products. Usage is assessed based on scenarios representative of Norwegian agricultural areas having different soil characteristics, precipitation and concentrations found currently in agricultural soil.

VKM has assessed current concentrations and in a 100-year perspective.

VKM has assessed the current limits in the Fertiliser Products Regulations for soil mixtures and has compared quality classes 0 and II to the value limits for EU-approved growth media, up against use for small growers of vegetables and for urban agriculture.

Findings

According to VKM, the use of fertiliser products containing potentially toxic elements can lead to more of these substances accumulating in the environment over time.

"We have estimated that concentrations of copper, mercury, lead and zinc will increase, in many regions, through the use of several of the fertilisers we have assessed," says Trine Eggen, scientific leader of the project team.

“The calculations show that the mercury level in the environment can increase by using the fertiliser products that we have assessed. This is not desirable, neither regarding the health of domestic animals or humans,” says Eggen.

She points out, among other things, that we lack knowledge about conversion to methylmercury and accumulation in the food chain. "There is particularly great uncertainty associated with mercury modeling," Eggen adds.

Eggen also points out that increased use of fertilisers originating from aquaculture and marine products can lead to a higher content of arsenic in the environment.

“Organic arsenic is not very toxic, but we lack knowledge about the conversion of organic to more toxic inorganic arsenic in the environment,” explains Eggen.

“Since the Norwegian population is already highly exposed to arsenic, cadmium and lead from diet, a further increase in these substances is undesirable,” says Eggen.

When it comes to animal feed, the current level of the most toxic substances - cadmium, mercury, and lead - is generally far below the levels that are considered as a risk to animal health.

According to VKM's calculations, the use of fertiliser products with potentially toxic elements could lead to the copper content in grazing plants increasing to a level harmful to the health of sheep at pasture. This applies to a 100-year perspective and especially for Hedmarksbygda Stange and alum shale areas. The addition of pig manure can further increase the copper level in pasture grass.

Uncertainty

Lack of knowledge makes the results uncertain. Among other things, there are few available analyses of current concentrations of potentially toxic elements in soil, surface water and crops. Sampling and procedures for analyses are not harmonized. There are only a few analyses that report on the current concentration of potentially toxic elements in fertilisers.

There is particularly great uncertainty in the assessment of arsenic, chromium, and mercury, where there is little knowledge about the presence and fate of different species of substances.

“There is a need for more data on heavy metals and arsenic both in agricultural soil, in surface water and in fertiliser products. Good risk assessments are completely dependent on a good data base,” says Eggen.

The risk assessment has been approved by VKM's Panel on Animal Feed.