Toxicity of aspen wood leachate to aquatic life: Laboratory studies

Abstract

Trembling aspen (Populus tremuloides Michx.), a common hardwood tree throughout Canada, is being harvested at increasing rates for use in paper and building materials. Piles of aspen logs have been observed to produce a dark, watery, acutely toxic leachate. A laboratory study was undertaken to elucidate the nature, strength, and persistence of aspen leachate toxicity and the chemical composition of the leachate. Leaching from aspen chips in the laboratory was rapid, with 1% mass loss in the first 24 h. Another 2 weeks of immersion was necessary to remove all remaining leachable material (3% total). Fresh aspen leachate derived from a 1:9 wood‐water mixture (35 d immersion) was characterized by amber color, low pH (4.0), extremely high BOD (>2,600 mg/L), and high conductivity (1140 μS/cm). The leachate was rich in phenols (30 mg/L), organic carbon (2,480 mg/L), and organic nitrogen (13 mg/L). Median acutely toxic concentrations of leachate were consistently 1 to 2% of full strength for trout and Daphnia. Inhibition of bacterial metabolism began at concentrations below 0.3%. Leachate was less toxic to plant life but inhibited algal growth at concentrations of 12 to 16%. Toxicity of aspen leachate persisted at the same level as in fresh leachate for more than 2 months unless artificial aeration was provided. Persistence was even greater at low temperature (5°C). Aged leachate underwent a transition marked by a rise in pH and dissolved oxygen concentration, a small decline in conductivity, and a color change, from amber to black. Toxicity declined abruptly when the supply of labile toxicants was exhausted, but it sometimes increased again from the products of microbial metabolism. Oxygen depletion, low pH, and phenolic compounds contribute to the toxicity of aspen leachate, but much of the toxic effect must be attributed to other, unidentified constituents.

Investigating Potential Toxicity of Leachate from Wood Chip Piles Generated by Roadside Biomass Operations

“…The remaining parameters of ammonia and pH showed no difference between sites but generally followed similar trends of decreasing ammonia and increasing pH over time. The latter observation is similar to findings from Taylor et al [23], who noted pH levels in aspen leachate became less acidic with increased exposure time. Organic compounds decreased over the exposure period but remained quite high (COD > 1000 mg¨L´1, TOC > 500 mg¨L´1 and color > 500 TCU).…”

“…Higher surface area to volume ratio of the smaller chips contributed to greater COD at Muldowan 22 [27]. Elevated COD levels are associated with increased toxicity as shown by previous work with aspen leachate [7,23], pulp mill effluent [28,29] and municipal landfill leachates [28,30]. True color also differed between sites, with the smaller chips from Muldowan 22 producing more highly colored leachate than the larger chips from Muldowan 18 (Mann-Whitney U = 1.00, p = 0.001) Although there were no significant difference in phenols between samples, there was an increase in phenols at both sites during the first spring sampling followed by a decreased over the remaining sampling period.…”

“…The static exposure consisted of placing 2 kg of wood chips in a polypropylene 1-cm opening mesh bag in 18 L of water for 28 days at room temperature and ambient light. The quantity of chips and water selected follows the 9:1 ratio of water to wood recommended by Taylor et al [23]. Static exposure tests were completed using duplicate samples of lodgepole pine, hybrid spruce, black spruce, and aspen.…”

Toxicity and chemistry of aspen wood leachate to aquatic life: Field study

“…In addition to dissolved sugars from the phloem (sap), the wood or bark may contain plant secondary compounds, such as phenols, resin acids, and terpenes. Industries such as pulp and paper manufacturing, as well as government regulatory bodies, have long been aware of potentially harmful leachates from woodyards, waste piles, and landfills [3][4][5][6][7], although relatively few reports have been published in the literature [8][9][10][11][12][13][14]. As the wood decays, toxic phenolic compounds may be released through the decomposition of lignin [2].…”

“…Taylor et al [11] undertook a laboratory study to determine the rate and quantity of leaching loss from aspen wood, the chemical composition of the leachate, and the strength and persistence of leachate toxicity. In that study, leachate from aspen wood chips (9:1 w/w ratio of water to wood) was characterized by low pH, high conductivity, and very high BOD, leading to persistent anoxia.…”