Abstract :
[en] This paper aims to focus on surprising results when assessing the human toxicity of corn farming in Wallonia, Belgium. The USEtox method is applied to the farming of 1 hectare of corn. Local data are used for farming data and GaBi datasets are used for background data. The field emissions due to farming are calculated by the most used models.
The results in human toxicity, cancer effect, underline the large contribution of chromium (Cr) emissions due to the use of organic and mineral fertilizers. But during fertilizers composition characterization only the total chromium is measured and therefore, unspecified chromium is used as emissions. However, it is known that the chromium in natural environment is most probably Cr (III) and this could really decrease the impact as the characterization factor for unspecified chromium, is, in USEtox, the average of the one of Cr (III) (non-toxic) and Cr (VI) (toxic), therefore really larger than the one of Cr (III). Therefore, a test is realized where 95% of the Chromium is Cr (III) and the rest is Cr (VI). In this case, score in human toxicity cancer effect is divided by 7, whereas this has no influence on the other results.
The impact for human toxicity, non-cancer effect is mostly related to zinc emissions in soil due to the use of organic fertilizer, especially pig manure. However, zinc is abundant and is an important trace element in the human body. It is useful for growth, bone and brain development, etc. and the European Commission recommends the consumption of 7- 10 mg of zinc by person and per day. Moreover, mammals are able to eliminate zinc, therefore they are able to maintain a constant level of zinc independently of the exposure level. Consequently, only the exposure to high doses can have toxic effects. A test was made with the characterization factor of zinc equal to 0 in the USEtox model. In this case, the corn cropping obtains a human toxicity, non-cancer effect divided by 12 compared to the base case and mostly related to lead and mercury emissions in the soil. In both case, the contribution of pesticide is negligible.
In conclusion, although the uncertainties about toxicity categories are well-known, this case study underlines the impact of the user hypotheses and shows that a detailed analysis of the results is essential for a critical view on the toxicity results.
