Acute toxicity tests with Daphnia magna were used to measure the toxicity of runoff from three major highway sections in Israel for 2 yr. Highway first flushes ...
Journal of Environmental Quality
TECHNICAL REPORTS Groundwater Quality
Daphnia magna Indicate Severe Toxicity of Highway Runoff Achik Dorchin and Uri Shanas* Road runoff is recognized as a substantial nonpoint source of contamination to the aquatic environment. Highway seasonal first flushes contain particularly high concentrations of pollutants. To fully account for the toxicity potential of the runoff, the cumulative effects of the pollutants should be assessed, ideally by biological analyses. Acute toxicity tests with Daphnia magna were used to measure the toxicity of runoff from three major highway sections in Israel for 2 yr. Highway first flushes resulted in the mortality of all tested individuals within 24 to 48 h. A first flush collected from Highway 4 (traffic volume: 81,200 cars d-1) remained toxic even after dilution to B.
reproduction rate, of D. magna and other cladocerans (Skinner et al., 1999; Cooper et al., 2009). We exclude a possible contribution of other nonmetal inorganic constituents to the runoff toxicity because they were controlled throughout the tests (e.g., pH, dissolved oxygen concentration) or were found in appropriate concentrations for aquatic biota (e.g., ion concentrations). Marwood et al. (2011) have demonstrated that tire and other road wear particles are not toxic to D. magna under standard temperature conditions. We also found a synergistic effect of metals in the synthetic solution HW70s. Metal concentrations in this solution were lower than the EC50 concentrations of each of the metals separately (Tables 1 and 3). Nevertheless, 48 h of exposure to this solution resulted in mortality of 75% of the individuals (Fig. 2). Burba (1999) showed a high susceptibility of D. magna to a mixture of heavy metals prepared with concentrations equivalent to the 96-h LC50 value of each of the tested metals. The 96-h LC50 of this metal mixture was as low as 1.1%. These additive and synergistic effects highlight the importance of using biological analyses for the detection of pollutants in general and in road runoff in particular.
Effects of Midseason Runoff The midseason runoff collected in our study did not affect D. magna survival. In contrast, some midseason runoff collected from southern California highways was found to have a toxic effect on the cladoceran Ceriodaphnia dubia (Katznelson et al., 1995; Kayhanian and Borroum, 2000). The lower toxicity of our midseason runoff may be due to the exclusion of the heavily polluted first flush phase because the runoff was collected several hours after the rain event had started. It is also possible that, although we did not observe an acute effect, chronic effects may be expected, similar to the ones found in aquatic vertebrates (Dorchin and Shanas, 2010).
Daphnia magna Relative Susceptibility to Road Runoff Contamination Daphnia magna (among other aquatic invertebrates) are more susceptible than aquatic vertebrates (e.g., fish) to heavy metals (Khangarot and Ray, 1987; Enserink et al., 1991; Mark and Solbé,
Table 3. Reference median effective concentration values (and 95% confidence limits) of metals for Daphnia magna compared with calculated metal concentrations in media from Highway 4 first seasonal flush. Heavy metal
Synthetic solution
48–96 h EC50† HW41st‡ (total)§
HW41st (soluble)
————————————————————————— mg L ————————————————————————— 54¶ 19.9 (14.5–27.4) 6.6 (4.8–9) 4400¶ (3600–5300) 3.8 (2.75–5.2) 1.3 (0.9–1.75) 2580# 3.6 (2.6–4.9) 0.9 (0.65–1.2) -1
Cu Pb Ni Medium properties
45 mg L-1 CaCO3; 19–21 (18 for Ni)°C; pH 7.5–8.5 74 mg L-1 CaCO3; 3 ± 1°C; pH 7.5–8.5
74 mg L-1 CaCO3; 23 ± 1°C; pH 7.5–8.5
† Median effective concentration. ‡ Highway 4 first seasonal flush. § Metal concentrations are calculated by multiplying the actual determined concentration with the proportion corresponding to the determined 48-h EC50 value (4.82%; 95% confidence limits, 3.5–6.63%). Total metal concentrations (mg L-1) were determined as Cu = 414, Pb = 78.6, and Ni = 74.5. Data are from Rechtman (2006). Soluble metal concentrations are presented in Table 1. ¶ Versteeg et al. (1997). # Burba (1999).
1998). Similar to vertebrates, the major pathway of metal uptake in Daphnia spp. is directly from the water, although some metals are also accumulated through dietary uptake (Barata et al., 2002; Yu and Wang, 2002; Hare et al., 2003; Tsz-Ki Tsui and Wang, 2007). As a result, D. magna were probably affected by aqueous and particulate-bond metals in our test runoff. Relatively higher amounts of organic material, found in the TVS analysis of the first flushes, could contribute to the toxicity of the runoff through particulate-bond metals in the sediment and through organic toxicants. Indeed, total metal concentrations in the first flushes were 1- to 4-fold (although in one sample for Ni 0.5) higher than the aqueous metals (values for HW41st are presented in Table 3). In contrast, a previous study showed that anurans B. viridis exposed to the same road runoff were probably affected only by the soluble metals and consequently survived (Dorchin and Shanas, 2010). Nonetheless, Robinson et al. (2003) suggested that although Daphnia species and other aquatic invertebrates use molting as a mechanism for losing metals, they may increase the exposure in their predators. This is a subject of concern due to the important part played by invertebrates in aquatic food chains.
Environmental Implications of Highway Runoff The extensive effects of roads on aquatic environments are well documented (Forman and Alexander, 1998; Spellerberg and Morrison, 1998; Trombulak and Frissell, 2000; Gunderson et al., 2005). Accumulating evidence suggests that roads are the major source of toxic chemical contamination impairing aquatic habitats (Beasley and Kneale, 2002, 2003; Reeves et al., 2008). We found that pollutant concentrations in highway first flushes were 0.57 to 7.86 times higher than concentrations previously found in urban first flushes from the city of Ashdod, Israel (Asaf et al., 2004). The extremely low EC50 (
