# Risk Assessment of Displaced Sediment by an Extreme Event Cyclone in a Peri-Urban Zone Using Bioassays and Analytical Chemistry

## TL;DR

This study assesses the risk of sediment displaced by a cyclone in New Zealand using bioassays and chemical analysis, finding low toxicity and typical agricultural contaminants.

## Contribution

The study combines bioassays and chemical analysis to evaluate post-disaster sediment risks in a peri-urban zone.

## Key findings

- Elutriates showed low toxicity and yeast assays showed typical activity levels.
- Chemical analysis confirmed historical contamination by DDT metabolites and plant sterols.
- Displaced sediment risk in the Waitangi catchment is considered low.

## Abstract

Hawke’s Bay in New Zealand was impacted by Cyclone Gabrielle in 2023, experiencing intense weather conditions and rainfall. Rivers and streams surged beyond their banks, displacing large amounts of sediment. The sewage treatment plant and industries in the Waitangi catchment, south of the city of Napier, were heavily impacted, making them potential sources of contaminants. The aim of this study was to investigate the risk of displaced sediments deposited south of Napier City, using bioassays and chemical analysis methods. Sediment samples were collected across a gradient between the coastline and the Waitangi Stream. The toxicity of chemically extracted or elutriate samples was assessed by Microtox®, mussel embryo–larval development, and aryl hydrocarbon and constitutive androstane receptor yeast two-hybrid assays. Targeted chemical analysis and automated identification and quantification system (AIQS-GC) methods were used to identify contaminants. The elutriates showed low toxicity and the yeast assays showed levels of activity like those previously reported. Chemical methods confirmed historical contamination by DDT and its metabolites DDE and DDD, as well as by plant sterols. Overall, the toxicity and chemicals detected are what would be expected from a typical agricultural soil. The risk posed by the displaced sediment in the Waitangi catchment can be considered low. Combining chemical and bioanalytical methods was an effective approach to investigate the potential risks of post-disaster contamination.