Respiration Responses of Earthworm to Soil Amended with Phenanthrene and the Nitrogen Heterocyclic Analogues

A disturbance in the normal physiology of soil macroinvertebrates can cause toxic impacts and/or disruption in mechanisms and rates of respiration. In this work, respiration rates of earthworms exposed to phenanthrene and its nitrogen heterocyclic analogs was investigated over a 30 and 90-d soil-contact-time. The study involved measurement and calculation of CO2 production by earthworms exposed to phenanthrene–N-PAHs amended soils. Data showed that N-PAH chemicals mostly affected the respiration rates of the earthworms compared to the homologous-PAH analog over time. The concentration–time plots showed greater respiration with increase in concentration over time. Calculated respiration inhibition-effect (%) revealed that phenanthrene had low degree of inhibition (27%) in the first 30-d at the highest concentration, while, NPAHs exhibited high degree of inhibitions (>45%) on respiration/physiological function of the exposed earthworms over the 90-d contact-time. Among the N-PAH chemicals, benzo[h]quinoline recorded >25% inhibition even at the lowest concentration (30-d). Statistical analysis of data revealed that N-PAHs maintained strong positive correlation on respiration response of the organisms with increased concentration and time (R2 = 0.803–0.997, p < .05). This suggests that N-PAH chemicals may have caused severe metabolic and physiological stress/inhibitions to soil organisms. Furthermore, the use of earthworm’s respiration rate in polluted soils could likely reshape the understanding of environmental stressors and serve as an early warning indicator for potential ecosystem shifts