Soil-to-plant transfer of conventional and emerging contaminants in organic fertilizers: a human health risk assessment

Nowadays, one of the big concerns in agriculture is maintaining soil fertility while ensuring food safety. When farmers apply fertilizers to their fields, they provide essential nutrients for crop production, but these materials may contain trace amounts of contaminants that can potentially be transferred through crops to human consumers. This thesis investigates whether consuming tomatoes grown in soils amended with fertilizers creates meaningful health risks for Italian consumers. We focused on three model contaminants representing different chemical families: cadmium (a toxic heavy metal), benzo(a)pyrene (a cancer-causing organic compound), and trimethoprim (an antibiotic used in livestock and poultry industries). These substances were selected not only because they may be present in agricultural fertilizers but also because understanding their behavior helps predict risks from similar compounds. Using the standardized RHIZOtest methodology (a laboratory bioassay that measures how contaminants move from soil into plant tissues) we grew tomato seedlings in contact with fertilized artificial soil under controlled conditions. We tested two types of fertilizer at two application rates: a standard agricultural dose and a conservatively reduced dose. The first fertilizer represented typical agricultural material with baseline contamination levels, while the second fertilizer was intentionally spiked with higher contaminant concentrations to simulate worst-case scenarios. Our experimental results showed that each contaminant behaved quite differently. Cadmium moved readily from soil into roots and then translocated to edible shoots with moderate efficiency. Benzo(a)pyrene, which is highly hydrophobic, was tightly bound to soil particles and hardly entered the plant tissues. Trimethoprim showed surprisingly limited uptake despite being relatively soluble, probably due to strong interactions with soil minerals or rapid microbial degradation. The results obtained show that all calculated health risk indices remained far below regulatory limits. The Hazard Quotient (a measure that compares actual exposure to safe reference doses) remained below 0.01 for all groups and scenarios, meaning exposure levels were at least 100 times lower than thresholds of concern. Children aged three to ten years showed the highest exposure relative to their body weight, but even for this sensitive group, the safety margin was still significant. The cancer risk from benzo(a)pyrene was negligible, many orders of magnitude below acceptable thresholds. This research shows that well-managed fertilizer can coexist with rigorous food safety standards and support the sustainable intensification of agricultural systems in a resource-constrained world.