# Toxicity of Landfill Leachate to Stream-Dwelling Benthic Macroinvertebrates

## TL;DR

This study examines how landfill leachate affects aquatic insects in coldwater trout streams, finding that high concentrations can be toxic.

## Contribution

The study provides new toxicity data for landfill leachate on specific benthic macroinvertebrates in a coldwater stream context.

## Key findings

- Brachycentrus caddisfly larvae showed 100% mortality at leachate concentrations above 70% after 24 hours.
- Benthic communities near the landfill were rated as good to excellent, with no significant impact observed.
- Leachate concentrations above 60% caused death in Brachycentrus within 2 days during 7-day tests.

## Abstract

Laboratory and field investigations were used to assess the toxicity of leachate from a closed sanitary landfill on benthic macroinvertebrates in coldwater trout streams located near a landfill in southeastern Minnesota, USA. Field-collected invertebrates were exposed to a range of concentrations (0–100%) of leachate during a series of 24 h and 7-day laboratory toxicity tests. Benthic macroinvertebrates also were collected from two stream sites on either side of the landfill and at a third site downstream to assess potential pollution exposure of the stream communities. Ten different taxa exposed to 100% leachate for 24 h exhibited survival ranging from 0 to 100%, with survivorship not correlated to published invertebrate pollution tolerance values. More extensive 24 h tests with the least tolerant Brachycentrus caddisfly larvae found 100% mortality at leachate concentrations > 70%, with the first mortalities observed after 3 h. Brachycentrus had 100% survival at leachate concentrations < 40%. During 7-day tests, Brachycentrus had 100% survival at all leachate concentrations of 40% and lower, but all Brachycentrus died after 2 days at concentrations of 60% and higher. Instream benthic communities, averaging 12 to 17 different taxa at the various stream sites, were rated from good to excellent based on biotic index values, with intolerant taxa present at all three stream sites. Landfill leachate has not impacted the benthic invertebrate communities in streams nearby, but leachate at higher concentrations has the potential to be toxic to a variety of local taxa.