Waterose: Pulp Mill Effluent and Mytilus edulis: Introduction


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The Effects of Pulp Mill Effluent on

Byssal Thread Production by the

Marine Blue Mussel Mytilus edulis

by Waterose

Section 1. Introduction:

The effects of treated and untreated pulp mill effluent were tested on the regeneration of byssal threads by the marine Blue Mussel, Mytilus edilus. The untreated effluent was diluted in natural seawater, by a factor of ten, for six solutions with concentrations of effluent from 10⁰ to 10^-5. The threads of the mussels were dissected at the exterior ventral edge, five replicates were grouped into each solution, and, the regeneration of byssal threads was monitored at an end-point of forty-eight hours to determine the dose-response curve. The water temperature and aeration were maintained at a constant level. The pH and the salinity were not adjusted for each solution.

The untreated effluent inhibited the regeneration of byssal threads with increasing concentrations from 10⁰ to 10^-3; however, at very low concentrations of 10^-4, the regeneration of byssal threads exceeded the regeneration in the seawater control. There was zero regeneration of byssal threads in the treated effluent which had a salinity of zero. The results were influenced by different levels of salinity, pH, conductivity, and spawning activities by the mussels in each solution. There were higher fatalities in solutions where spawning had occurred.

Key Words:

Pulp Mill Effluent, Blue Mussel (Mytilus edilus), Byssal Threads Regeneration

Hypothesis:

The organisms will be tested for physiological response to both treated and untreated pulp mill effluent. The hypothesis for both types of effluent is:

H_O: Pulp mill effluent does not impair the generation of byssal threads by Blue Mussels.
H_A: Pulp mill effluent does impair the regeneration of byssal threads by Blue Mussels.

1.2 Introduction:

The discharge of effluent from pulp and paper mills into the marine environment is a serious concern in British Columbia (BC). The presence of harmful levels of dioxins and furans in fish and shellfish caused the closure of commercial shellfish fisheries in 1988 (Fisheries, 1997). Consequently, the federal government introduced regulations to reduce and eliminate harmful contaminants that are associated with effluent from pulp and paper mills that use chlorine in the paper bleaching process. These concerns include dioxins, furans, total dissolved solids (TDS), biological oxygen demand (BOD), adsorbable organic halogens (AOX), dissolved organic carbon (DOC), resin acids, chlorates, metals, chelating agents, salts, and naturally occurring toxic compounds that originate in the wood (CEPA, 1991). The introduction of new technology in BC pulp and paper mills, has reduced the loading of dioxins and furans by 95-99 percent between 1989 and 1996 (Fisheries, 1997). This was achieved primarily due to the shift from elemental chlorine bleaching to elemental free chlorine bleaching (Cross, 1998). Environment Canada advises that 46 percent of the total area, that was previously closed to shellfish harvesting in BC, has been re-opened (Fisheries, 1997).

This report is based on the analysis of the effects on Blue Mussels, (Mytilus edilus), of the treated and untreated effluent discharged from the pulp and paper mill located at Crofton, B.C. The monitoring programs in BC are vigilant. One method is to measure the levels of toxicants in the tissues of marine organisms. There are several types of organisms in the marine ecosystem that are useful to monitor because they have different feeding habits and occupy different niches. For example, some organisms occupy the middle to upper water column whereas others are bottom feeders. Crabs are active bottom scavengers that occupy the intertidal zone. The hepatopancreas of the crab is commonly used as an indicator of toxicant levels (Environment, 1996). The Environment Canada Dioxin and Furan Compliance Report released in 1996 reports that dioxin and furan levels in the hepatopancreas dropped from 159.1 parts per trillion (ppt) in 1990 to 45.1 ppt in 1994 for the effluent discharge by the Crofton mill. Similarly declines were reported in oysters; 29 ppt in 1989 to 0.2 ppt in 1993.

This experiment analysed the effects of the effluent on the Mytilus edulis, Blue Mussel. The physiological growth response of byssal thread regeneration was monitored in treated effluent and in different concentrations of untreated effluent. This species is commercially harvested in BC and is a typical representative of the filter feeder shellfish common to the BC coast. The Blue Mussels were selected because they are: established in the local waters of Vancouver Island, abundant, easy to obtain, easy to identify, and easy to maintain in the laboratory environment for the study period. Furthermore, they are a good representative species of filter feeders commonly found in sheltered bays where BC pulp mills are located.

Mytilus edulis is a blue coloured bivalve from the class Mollusca, family Mytilidae (Kozloff, 1983). It is commonly referred to as the Blue or European Mussel and is found in the temperate waters, of both the northern and southern hemispheres. Blue Mussels inhabit sheltered marine environments as dense aggregates attached to rocks or wooden submerged structures, such as the underside of docks. Mussels attach themselves to substrates by generating byssal threads, which are tough stringy fibres of protein, from the byssal gland. The protein attaches to many types of soft surfaces, both natural and man-made. It also has the potential application of cell immobilisation for tissue, such as bone, teeth, and soft tissue.

Mussels are shallow water organisms that can occupy a niche to a maximum depth of ten meters, although they are abundant near the low tide level, where the food supply of micro-algae is the concentrated. Mussels populate marine embayments, estuarine areas, and aquatic habitats adjacent to river mouths. They experience variable growth rates and high mortality rates when they are subjected to freshwater runoff. The Blue Mussel is a temperate water species and exhibits maximum growth rates within a temperature range of 16-22 degrees Celsius (dC). Extreme and abrupt changes in water temperature can trigger spawning behaviour and this can cause mortality because of the energy required to reproduce (Jamieson, 1986). Mussels require a minimum oxygen saturation of sixty percent (Newell, 1989).

The mussels were tested for physiological response to treated and untreated pulp mill effluent. The performance of the byssal gland was assessed to determine if pulp mill effluent interferes with the �normal� formation and regeneration of byssal threads. When dislodged from its� substrate, this species attempts to re-attach by the secretion of byssal threads from the byssal gland. The success in byssal thread attachment depends on the bioenergetics of the mussels, including the available energy reserves and allocation of energy between all physiological and biochemical processes. If the mussel has to use energy to compensate for an environmental stressor, then the mussel will have less energy available to regenerate byssal threads (Bright, 1998).

A significant amount of work in this area has been completed by M. Salazar of Applied Biomonitoring, in Kirkland, Washington. Byssal thread production, bivalve survival, and growth, are used to monitor exposure-dose-response because these types of growth are easily measured and understood (Salazar, 1998). Unfortunately, it was not possible to obtain experimental results published by Mr. Salazar.

A preliminary search for experiments involving the regeneration of byssal threads by mussels indicated the following. The regeneration of byssal threads in the freshwater mussel, Dreissena polymorpha, increased proportionally to increased temperatures (Clarke, 1996). The regeneration of byssal threads onto a PVC pipe from the marine mussel, Mytilus edulis, was enhanced by an iron compound stimulant and conversely inhibited by a compound repellent (Etoh, 1997).