Patrick Reynolds, PhD

Environmental Consultant & Website Designer
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Effects of Atmospheric Pollution on a Front Line Species

INTRODUCTION
Atmospheric pollutants such as industrial emissions, crop sprays can be deposited long distances from their points of release. There are three routes of entry for such pollutants into animals: respiratory absorption of inhaled airborne material, skin absorption from contact with contaminated substrates, and absorption through the gut from the ingestion of contaminated material. The experiments described here are concerned with absorption due to ingestion and contact. The effects of acidic gases such as sulfur dioxide on epiphytic lichens and algae have long been known. Recently it has become apparent that these organisms can accumulate large amounts of other atmospheric pollutants such as heavy metals, organic compounds, and radionuclides. Many arthropod assemblages are associated with epiphytic algae and lichens, most using these as a source of nutrients. In this study one such group, the bagmoths (Lepidoptera: Psychidae), were used for measuring biological effects of atmospheric pollutants. Bagmoth larvae were used as they constitute a "front-line" or sentinel group of indicator organisms because of the ability of their algal diet to absorb large quantities of atmospheric pollutants.

The global distribution of the Psychidae ranges from Finland to the tip of South America. They are commonly referred to as bagmoths because their larvae construct portable dwellings from silk coated externally with their various pabulae. These bags protect the larvae from desiccation and provide them with camouflage enabling them to avoid the attention of predators.

MATERIALS AND METHODS
Test Organism
The species of bagmoth used for this work was Luffia ferchaultella on account of its size and features of its life cycle and biology, notably that it reproduces by parthenogenesis. Its larvae feed on terrestrial epiphytic algae of the Pleurococcus group. Larvae were collected from a woodland (UK OS Map Ref. SU 769 855) and reared in the laboratory on a diet of epiphytic algae (Pleurococcus sp.) under controlled environmental conditions [20.8 (20.6-21.0)oC, photoperiod 14 h light, 10 h dark].

Experimental Design
The practical work was divided into two phases: (1) a laboratory-based simulation of contamination due to atmospheric pollution, designed to investigate the sensitivity of the test organism; (2) collection of samples along an impacted transect followed by an investigation of their toxicity using the protocol derived during the first phase.

RESULTS
Laboratory-Based Spray Drift Simulation
The results for feeding of bagmoth larvae exposed to pesticide-amended algae showed that exposure of the bagmoth larvae to lindane resulted in a classic dose-response relationship. The no-observed-effect concentrations (NOECs) ranked as follows: 1st. feeding, 2nd immobility and 3rd mortality (Table 1).

bagmoth, patrick-reynolds, Luffia-ferchaultella


Feeding was the most sensitive endpoint examined, the 10-day NOEC (feeding) being 1.7 ug/g algae. With aldrin, the three endpoints produced common NOECs of 7.5 ug/g algae. Effects were not seen at lower concentrations as all larvae remained mobile, with no inhibition of feeding observed below the NOEC. Permethrin was the least toxic of the three pesticides examined. No significant mortality or immobilization occurred at any of the treatments, but feeding was adversely affected at 24 ug/g algae, the NOEC (feeding) being 8.1 ug/g algae.

Luffia-ferchaultella, bagmoth, patrick-reynolds

To understand these toxic effects further the body burdens of these substances in affected larvae were examined. The body burden data (Table 2) indicated that exposure of the larvae to lindane at 102 ug/g in their diet resulted in accumulation of 2.7 ug/g in the larvae, 20% mortality, and complete immobilization after a 10-day exposure period. Exposure of the larvae to aldrin at 95 ug/g in the diet resulted in their accumulation of diedrin, presumably by an epoxylation reaction similar to that observed with plants and soil , although in this study dieldrin was not detected in the spiked algae. At this treatment a total body burden of 5 ug/g aldrin and 22 ug/g dieldrin killed 60% of the larvae and immobilised a further 20% after a 10-day period. Permethrin was not detected in the larvae exposed to the highest concentration (204 ug/g algae), which caused only reduced feeding and 20% immobility when compared with the controls. This indicates either that larvae failed to absorb permethrin from the algae or that larvae metabolised permethrin rapidly to substances of low toxicity that were not detected using the analytical techniques described above or otherwise eliminated it.

pesticides-bagmoth-body-burden, patrick-reynolds


Exhaust Emission Simulation
The results for exposure of bagmoth larvae to algae amended with vehicle exhaust gases showed that the lead content of the algae increased with increasing time of exposure to exhaust gas/air mixture. Larvae exposed to algae containing lead at 200 ug/g and above did not feed during the 96-h exposure period, by which time they had become immobilized.

Field Transect
Lead concentrations in the algae were highest at the downwind site closest to the M40 (site 4), and declined gradually with increasing distance downwind from the motorway. Chromium concentrations were elevated at both sites closest to the motorway (sites 3 and 4), but were higher downwind than upwind. Algae from the control site contained less lead and chromium than at any of the transect sites. Feeding was reduced at site 4, the closest downwind site (10 m) to the M40, where the concentration of metals was highest. Feeding increased at sites 5 and 6, further downwind of the M40 (300 and 700 m, respectively). Feeding was also depressed at site 1, an area surrounded by arable farmland located furthest upwind of the M40 (700 m), but increased upwind of the M40 as the sites approached the motorway and distance increased from the farmland (sites 2 and 3, located 300 and 10 m from the M40, respectively). It is significant that larvae supplied with algae from the "clean" control site, an isolated rural woodland far removed from arable farming and the influence of road traff|c, fed much more than those supplied with algae from the transect sites. This is evidence of the impacted nature of the environment along the transect. However, traces of lindane (0.2 ug/g algae) were found in samples of control algae analysed prior to spiking, indicating that the control site was not pristine.

DISCUSSION
The most important feature of this work is that epiphytic algae have a high affinity for atmospheric pollutants and that bagmoth larvae feed on this material. This makes them front-line or sentinel indicator organisms as far as the toxicological effects of airborne pollutants are concerned. The epiphytic algae Diplococcus sp., on which Luffia ferchaultella feeds, can be attached to filters and used to absorb pollutants from an air stream. This material can then be used to establish air / algae equilibrium kinetics and for laboratory feeding trials. Laboratory experimentation has demonstrated that bagmoth larvae are adversely affected by common atmospheric pollutants absorbed by this material. Feeding was found to be the more sensitive of three toxicological endpoints investigated. The metabolism of aldrin to dieldrin, detected by analysis of larval body burdens, is significant when one compares the toxicity of aldrin with that of lindane. As the average third instar larval wet body weight was 1.5 mg, we calculate that the lethal quantity of aldrin ingested over a 10-day period was 35 ng/larva. The corresponding value for lindane was 1ng. The lethal dose for permethrin could not be calculated because of its low toxicity to these organisms. A subsequent field investigation using a transect across an impacted environment identified that reduced feeding by bagmoth larvae was related to proximity to sources of atmospheric pollution. The presence of large quantities of heavy metals in samples collected near a motorway confirms the ability of epiphytic algae to accumulate heavy metals from the air. The high concentrations of chromium and lead proximally downwind of the M40 indicate the strong effect of prevailing wind direction in dispersal of pollution from motorway traffic at this locality. Lead is a commonly used additive in petrol, while chromium is an additive used in the cement that this section of the M40 was surfaced with at that time. The detection of measurable amounts of lindane in algal samples collected from a "clean" site demonstrates the ability of these unicellular plants to accumulate this and probably other organic substances from the atmosphere.

CONCLUSIONS
There are many features of the biology of Luffia ferchaultella that make it a useful organism in ecotoxicological studies. Of most importance for assessing the toxic effects of atmospheric pollutants is that the diet of its larvae is capable of sequestering such pollutants, resulting in measurable detrimental effects on their feeding. Results of laboratory experiments designed to simulate pollution from agricultural sprays and vehicle exhaust emissions identified feeding as the most sensitive endpoint of those examined. A field transect demonstrated that larvae supplied with algae collected from an environment impacted by atmospheric pollution exhibited reduced feeding compared with those fed algae from a "clean" control site.