Assessment of Heavy Metals in Organic and Non-Organic Vegetables Post Severe Tropical Cyclone Gabrielle: A cross-sectional comparative analysis

Abstract

Background Heavy metals such as cadmium, lead, and mercury are ubiquitous in the environment, accumulating in plants, animals, water and human food. Human exposure through the consumption of vegetable crops is a global concern because such metals may be toxic even in trace amounts. There are many factors influencing heavy metal concentrations in vegetables including, soil properties, growing practices and flooding events. This study aimed to investigate heavy metal concentrations in vegetable samples in Hawke’s Bay, New Zealand, one year post Severe Tropical Cyclone Gabrielle, which caused widespread flooding on the 14th of February 2023.

Methods This cross-sectional study included organic and non-organic vegetables and sites impacted and not-impacted by cyclone flooding. In total, 736 vegetable samples were combined to form 153 representative samples collected from 14 markets grown at 10 growing sites. Samples were analysed by ICP-MS in an ISO-17025 accredited laboratory.

Results Cadmium (p = 0.003) and nickel (p < 0.001) contamination were higher in non-organic vegetables. Growing vegetables on flood-affected land was independently associated with reduced cadmium (p = 0.030) and nickel (p = 0.024) contamination. Three samples exceeded Codex Alimentarius lead permissible levels (0.1 mg kg−1 fresh weight), and one sample exceeded cadmium permissible levels (0.05 mg kg−1 fresh weight in Brassica).

Conclusions This study suggests that Hawke’s Bay vegetables by global standards, are generally low risk, for heavy metal toxicity and organic vegetables, carry the lowest risk. However, some vegetables do exceed maximum limits for lead and cadmium. We speculate that recent Severe Tropical Cyclone Gabrielle did not increase risk and may have reduced the risk of heavy metal toxicity from vegetable consumption.