THE FACTS ABOUT EFFLUENT TOXICITY
By Pulp & Paper Canada
By Pulp & Paper Canada
Several pulp and paper mills across Canada have been legally charged for failing their effluent toxicity limits, and this trend is likely to continue if regulators feel public pressure to enforce envi…
Several pulp and paper mills across Canada have been legally charged for failing their effluent toxicity limits, and this trend is likely to continue if regulators feel public pressure to enforce environmental regulations. The following is intended to put effluent toxicity into perspective, for the sake of regulators, toxicity testing laboratories and the industry.
Mill managers — pay attention: According to Canadian law and most provincial environmental regulations, the consequences of a toxicity test failure are serious. For example, the Fisheries Act can be used to charge mill managers personally, and fines can be in the hundreds of thousands or millions of dollars. In Quebec, the “Loi sur la qualit de l’environnement” states that the maximum charge for one test failure is $500 000 and the minimum is $25 000. In the past five years, several senior managers have been personally charged for effluent toxicity failures.
To avoid spending too much time with expensive lawyers and expert witnesses, mill managers should pay close attention to preventing and reacting quickly to toxicity test failures. In the end, it may be cheaper and much less damaging to the environmental image of the corporation and the individual. As we know, media reports will not be in the company’s favor and will probably make it sound as though the mill effluent killed many fish in the receiving environment — not very good for shareholders and the public.
WHAT DOES TOXICITY REALLY MEAN?
In reality, the effluent probably only killed six to 10 small trout (usually 3 to 5 cm long) or the same number of microscopic Daphnia magna (water flea) that have been swimming in a container of 100% effluent for four days (for trout) or two days (for Daphnia). That is the definition of effluent toxicity according to Environment Canada test methods used by toxicity testing laboratories. Furthermore, when a mill fails a toxicity test, the environmental impacts are typically negligible because the effluent is usually diluted to non-toxic levels as it enters receiving waters. Fish mortalities in receiving environments due to discharges are rare and usually occur following chemical spills directly to the receiving water, without treatment.
To recap: effluent toxicity means that during a controlled toxicity test performed by a contract laboratory, six or more of the 10 test organisms (rainbow trout fry or Daphnia magna) died after exposure to 100% effluent in a test vessel. The irony is that even if there are no environmental effects, companies and individuals can be charged and pay fines.
WHY DOES TOXICITY OCCUR?
The main causes of test failure are the following:
1. Poor internal spill control, and excessive losses of black liquor, chemicals and BOD to the treatment plant, causing a decrease in the BOD removal efficiency (and toxicity removal) of the secondary treatment plant.
2. Toxic residual levels of un-ionized ammonia and/or hydrogen sulphide in the final effluent.
3. Residuals of other chemicals in the effluent. These can sometimes be difficult to identify.
4. Poor sampling procedures and effluent contamination.
5. A lack of quality assurance and quality control by the testing laboratory.
Many of these causes can be minimized or prevented within the framework of an environmental management system, by putting in place the right procedures and training programs, and having environmental objectives and targets to minimize spills and losses to the treatment plant. Contract laboratories should also be audited regularly by an outside third party (laboratory auditor) retained by the mill.
TOXICITY TEST VARIABILITY
In inter-laboratory studies on coded samples, the coefficient of variation (C.V.) between laboratories performing toxicity tests is typically 30% to 50%. This means that, for a C.V.=30%, a test on any given sample could vary from an LC50 of 25%v/V to 100% v/v, or from moderately toxic (fail) to non-toxic (pass). Performance evaluation studies conducted across Canada by Canadian Association of Environmental Analytical Laboratories (CAEAL) in 1997 and 1998 showed this type of variability among over 90 participating laboratories. Hence, it is not uncommon that test results from different toxicity laboratories on the same sample will be quite different. In some cases, a sample may pass the test at one lab and fail at another. Although Environment Canada test methods are detailed, there can be variability due to the following:
Differences in laboratory water quality and organism holding conditions.
The stock of fish used, their weight, length and sensitivity. There can be a significant difference in the sensitivity of 0.3 g fish and 5.0 g fish (the acceptable size range for testing).
Temperature changes and time delays between effluent sampling and the start of the test (this can change effluent composition).
The level of competence and training of laboratory technicians performing the test.
The level of quality assurance and quality control is critical for toxicity tests. At a minimum, labs should be ISO Guide 25-accredited for both the trout and Daphnia tests. However, mills should also do their own verifications and make expectations clear to their testing labs. For example, it may be desirable to use fish that are above 0.6 g (instead of 0.3 g) in weight and only use test fish that show a pre-test mortality of less than 1% in holding tanks (instead of 2%).
Another common problem is the lack of statistical analyses applied to test results. In many cases, toxicity test results show no partial mortalities in the various effluent concentrations tested (i.e. one control and five test concentrations). In such cases, a binomial analysis is used, which is a straight arithmetic calculation that does not deal with test variability. To obtain more reliable test results, the number of effluent dilutions (to obtain partial mortalities) should be increased so that regressions and estimates of variability can be calculated. Test replication will also produce a better data set and remove ambiguity in the test results. At a maximum fine of $500,000 per test failure, it is worth paying a little extra for the test and obtaining more statistically robust data.
The best strategy for preventing toxicity problems is tight in-mill spills control, environmental awareness of staff, effective BOD removal during secondary treatment, and low levels of total ammonia and hydrogen sulphide in the final effluent (i.e. no anaerobic activity and sufficient oxygenation in the treatment plant). An Effluent Toxicity Prevention and Remediation Plan, which addresses all the above issues, should be part of the mill’s environmental management system. P&PC