Supervising Scientist Environmental Monitoring Program

Explanatory notes on toxicity monitoring

History of Toxicity Monitoring

In this form of monitoring, effects of runoff water from the Ranger uranium minesite on receiving waters are evaluated using responses of aquatic animals exposed to creek water. More information about the research originally conducted to develop these tests can be found in the Supervising Scientist Annual Report 2000–2001 (pp 49–50) section 3.1.4.

From the 1991-92 through to the 2005-06 wet seasons, the freshwater snail (Amerianna cumingi) and the larvae of black-banded rainbowfish (Melanotaenia nigrans) were used for toxicity monitoring. The endpoints of the tests were reproductive output (egg production) and larval survival, respectively. However, the fish test was not only much less sensitive than the snail reproduction test to uranium and magnesium in Ranger minesite water, but the fish larvae also suffered much higher (natural) mortality rates at the upstream control site, compared with
the downstream 'exposed' site. For these reasons, routine testing using the fish larvae was discontinued in the 2006/07 wet season, with resources directed towards developing improved toxicity monitoring techniques (such as in situ methods, discussed below) and continuous water quality monitoring (see Supervising Scientist Annual Report 2007–2008 (pp 52–60), section 3.2).

Toxicity monitoring is conducted in Magela Creek  upstream of the mine (control site) and at an ‘exposed’ site located approximately 400 m downstream of the gauging station GS8210009, some 5 km downstream of a point directly adjacent to the mine (see map). The sites are the same as those at which the SSD collects water chemistry samples and associated information (grab samples and continuous data).

The creekside technique (Figure 1A) provided the primary means for toxicity monitoring from 1991–92 through to the 2007–08 wet season. Creekside monitoring used water pumped from the creek to header tanks located on the bank. The water stored in the header tanks provided continuous water flow to chambers (aquaria) containing the test organisms.

At the end of each four-day test, the mean number of eggs per snail pair (and previously, mean number of fish surviving per replicate), are noted and compared between the upstream and downstream sites. Specifically, when data from the downstream site are subtracted from those at the upstream site, a set of 'difference' values are derived. These difference values may be compared statistically for different parts of the time-series. For example, 'difference' data for the current wet season  may be compared with those from previous years.  If a significant difference is detected, using an ANalysis Of VAriance (ANOVA) test, it may indicate a mine-related change - with more detailed investigative work triggered. Technical details of the statistical design and data analysis procedures may be found in Humphrey et al (1995), in Appendix 4, volume 2 of ANZECC and ARMCANZ (2000), and in the paper ‘Toxicity monitoring in Magela Creek’ located in the eriss research summary 2007–2008.

Following three years of development, which included two years comparative testing, the creekside monitoring technique was replaced by an in situ monitoring (Figure 1B) method. In situ monitoring uses floating test chambers tethered in the creek, requiring greatly reduced test infrastructure and staff resources while providing improved water flow-through and contact conditions for the test organisms. This technique is also portable and potentially, may be readily deployed at new testing locations.

The results of the comparative testing conducted during the 2006–07 and 2007–08 wet seasons showed that the upstream-downstream ‘difference’ values between in situ monitoring and creekside monitoring were directly comparable (no significant difference between the ‘difference’ data). Most importantly, the results demonstrated that results from the in situ technique would be comparable with the time series of data collected since the 1991–92 wet season using the creekside method. The in situ method using freshwater snails replaced the creekside method from the commencement of the 2008–09 wet season. For further details of the comparative study, see ‘Development of in situ toxicity monitoring methods for Magela Creek’ in the eriss research summary 2007–2008.

Some limited additional evaluation of the fish larvae method was done during the 2006-07 and 2007-08 wet seasons. Testing was confined to the upstream site to determine if the high mortality rate observed at this site during earlier years was specifically attributable to features of the creekside methodology, and whether survival could be increased. Comparison of the results from creekside and in situ deployment showed that there was no improvement in the larval fish survival when using the in situ monitoring technique. Because the in situ monitoring technique did not resolve the high upstream mortality in larval rainbowfish and because the fish larvae are not nearly as sensitive as snails to Ranger mine waters, this test is no longer conducted as part of the Ranger mine toxicity monitoring program.

Currently the response of one test species is employed, namely, reproductive output (egg production) of the freshwater snail, Amerianna cumingi, measured over test periods each of four days using the in situ deployment method.

Results to date

Snail egg production

Since their inception in 1991–92, toxicity monitoring tests have been performed approximately every other week (ie once a fortnight) during the wet season. Tests usually commence in December and cease in early April, the period of significant flow in Magela Creek. The results of the toxicity monitoring tests are plotted as part of a continuous time series of actual response and paired-site (upstream-downstream) 'difference' data. Figure 2 displays toxicity monitoring data for freshwater snail egg production acquired using the in situ testing procedure that has been deployed since the 2006–07 wet season. Data collected from 1991–92 to 2007–08 using, primarily, the creekside monitoring procedure, are available in the archived plot.

Results are reported and discussed in detail on an annual basis (see respective Supervising Scientist Annual Reports). Results for 2009–10 are preliminary and will be analysed and discussed in further detail at the end of the wet season.

For the 2009-10 wet season, continuous surface flow in Magela Creek commenced on 25th December (2009). Since the establishment of continuous flow, three in situ toxicity monitoring tests have been completed: 4th – 8th January, 18th – 22nd January and 1st – 5th February (2010). The results for the first two tests show concordance with data from previous years. However, the third test produced the third largest difference value reported since testing commenced in 1991-92 (see historical data). The large difference value is due to a greater proportional decline in egg numbers at the upstream site (Figure 2). For this period of testing, routine and continuous water chemistry monitoring in Magela Creek indicate conditions typical of outflowing of previously-ponded waters from billabongs located between the upstream and downstream site. Such conditions are not uncommon following a fall in Magela Creek water levels after flood or high-flow events. It is probable that the increased influence of billabong waters during the third test, as a result of the falling water levels in the creek, provided more favourable contact waters for the downstream snails by way of either more (mine-derived) dissolved solutes (MgSO₄, Ca) or increased nutrients and natural organic matter that supplements their food supply. This greater food supply would, in turn, enhance egg production and thereby explain the reduced decline in egg production observed at the downstream site relative to upstream.