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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The ecological properties of ferrous slag are virtually the same as these of natural rock e.g. basalt, diabase, granodiorite, and greywacke.  Ferrous slag is not toxic to algae (nominal):
OECD TG 201 (Alga, Growth Inhibition Test) using Desmodesmus subspicatus
ABS: 72 h-IC10 >= 32 g/L, the IC50 is > 94 g/L
ABS from toploader kiln (2 samples): 72 h IC0 >= 100 g/L, the IC50 > 100 g/L (highest concentration tested)
ABS: 72 h-NOEC >= 100 mg/L, the EC50 > 100 mg/L (highest concentration tested; disregarded for assessment).
GBS: The 72 h-IC0 >= 100 g/L, the IC50 > 100 g/L (highest concentration tested)
BOS (2 samples): 72 h-IC10 = 19 g/L, 72 h-IC50 > 100 g/L (highest concentration tested) and 72 h-IC10 = 19 g/L, the 72 h-IC50 = 86 g/L
EAF C: 72 h-NOEC >= 10 g/L, 72 h-EC50 > 10 g/L (highest concentration tested)
EAF C: 72 h-IC10 =15 g/L, the 72 h-IC50 = 42 g/L
EAF S: 72 h-NOEC >= 10 g/L, 72 h-EC50 > 10 g/L (highest concentration tested)
SMS, ladle slag: 72 h-IC10 = 0.25 g/L, 72 h-IC50 = 2 g/L (disregarded for assessment)
SMS, desulfurization slag: 72 h-IC10 = 24 g/L, 72 h-IC50 = 90 g/L
OECD TG 201 (Alga, Growth Inhibition Test) using Pseudokirchneriella subcapitata
BOS: 96 h-EC50 >17.75 g/L (reported as < 17.75 g/L)
SMS: 96 h-EC50 >17.75 g/L (reported as < 17.75 g/L)
DIN 38412-L33 (Alga, Growth Inhibition Test) using Desmodesmus subspicatus
ABS (2 samples): 72 h NOEC >= 80 g/L and > 50 g/L
BOS: 72 h NOEC >= 80 g/L
EAF C: 72 h NOEC >= 80 g/L
The ecological properties of slag are virtually the same as these of natural rock e.g. basalt, diabase, granodiorite, and greywacke.
NF EN ISO 28692 (Alga, Growth Inhibition Test) using Pseudokirchneriella subcapitata:
ABS (2 samples): 72 h-NOEC >= 90 g/L
EAF C: 72 h-NOEC = 11 g/L
EAF S: 72 h-NOEC = 18 g/L
Field and fertilizer studies supported that conclusion. Key values were derived taking into regard ample evidence (presented below) for case to case decision.

Key value for chemical safety assessment

EC50 for freshwater algae:
80 g/L
EC50 for marine water algae:
8 g/L
EC10 or NOEC for freshwater algae:
32 g/L
EC10 or NOEC for marine water algae:
3.2 g/L

Additional information

To elucidate the toxicity of ferrous slag to algae, several slags were tested on various algae in growth inhibition tests:

OECD TG 201 (Alga, Growth Inhibition Test) using the freshwater alga Desmodesmus subspicatus (formerly Scenedesmus subspicatus) (equal to C.3 Algal Inhibition Test of the EU-Regulation 440/2008)

ABS: The 72 h-IC10 is >= 32 g/L, the IC50 is > 94 g/L (nominal, Hygiene-Institut des Ruhrgebiets 2002)

ABS from toploader kiln: The 72 h IC0 is >= 100 g/L, the IC50 is > 100 g/L (nominal, highest concentration tested) (Hygiene-Institut des Ruhrgebiets 2003)

ABS from toploader kiln: The 72 h IC0 is >= 100 g/L, the IC50 is > 100 g/L (nominal, highest concentration tested) (Hygiene-Institut des Ruhrgebiets 2008)

ABS: The 72 h-NOEC is >= 100 mg/L, the EC50 is > 100 mg/L (nominal, highest concentration tested; this value is disregarded for assessment because the insolubility of the slag is a desired property of the slag for its use in construction. The low solubility was the reason why the experiments were ordered to be made with extremely low concentrations instead of concentrations relevant for the environment) (Hygiene-Institut des Ruhrgebiets 2009)

GBS: The 72 h-IC0 is >= 100 g/L, the IC50 is > 100 g/L (nominal, highest concentration tested) (Hygiene-Institut des Ruhrgebiets 2000)

BOS (2 samples): For the first BOS, the 72 h-IC10 is 19 g/L, the 72 h-IC50 is > 100 g/L (nominal, highest concentration tested). For the second BOS, the 72 h-IC10 is 19 g/L, the 72 h-IC50 is 86 g/L (nominal). (both: Hygiene-Institut des Ruhrgebiets 2001)

EAF C: 72 h-NOEC >= 10 g/L, 72 h-EC50 > 10 g/L (nominal, highest concentration tested) (Fresenius 2010)

EAF C: 72 h-IC10 is 15 g/L, the 72 h-IC50 is 42 g/L (nominal) (Hygiene-Institut des Ruhrgebiets 2001)

EAF S: 72 h-NOEC >= 10 g/L, 72 h-EC50 > 10 g/L (nominal, highest concentration tested) (Fresenius 2010)

SMS, ladle slag: The 72 h-IC10 is 0.25 g/L, the 72 h-IC50 is 2 g/L (nominal). There is no explanation for and no verification of the unexpected result given by the authors (Hygiene-Institut des Ruhrgebiets 2002)

SMS, desulfurization slag: The 72 h-IC10 is 24 g/L, the 72 h-IC50 is 90 g/L (nominal) (Hygiene-Institut des Ruhrgebiets 2002).  

 

OECD TG 201 (Alga, Growth Inhibition Test) using the freshwater alga Pseudokirchneriella subcapitata (species reported as Selenastrum capricornutum)

To check the toxicity of slags to algae, BOS were tested on the freshwater species Pseudokirchneriella subcapitata (green algae) according to OECD TG 201. Tests were performed using a L/S (liquid/solid) of 4/1 leachate (0.25 kg of slag/L of leaching medium) at 5 concentrations: 6.25 %, 12.5 %, 25 %, 50 % and 100 %. The leachates were neither neutralized nor filtered. The controls were sterile, and there is no information how the slag leachate inocula were kept sterile. The 96 h-EC50is >17.75 g/L (nominal; reported as < 17.75 g/L but evidence presented by IUCLID editor that > is meant). As algae tolerate only a limited pH range, these experiments indicate some pH influence. However, the results confirm that slags exert no acute toxicity to algae. The same result was reported for SMS (Reis da Silva et al. 2006, 2007).

 

DIN 38412-L33 (Alga, Growth Inhibition Test) using the freshwater alga Desmodesmus subspicatus

Leachates of several slags used in waterway construction, were prepared according to DIN 38414-4, DEV-S4. After neutralization, during 72 h of incubation the following results were obtained:

ABS (2 samples): For the first ABS, the NOEC was >= 80 g/L nominal, which was the highest tested concentration (BfG 2008 Manz). For the second ABS, the NOEC was > 50 g/L nominal (BfG 2008 Mueller)

BOS: In a 72 h incubation, the NOEC was >= 80 g/L nominal (BfG 2008 Mueller)

EAF C: In a 72 h incubation, the NOEC was >= 80 g/L nominal (BfG 2008 Mueller)

The ecological properties of slag are virtually the same as these of natural rock e.g. basalt, diabase, granodiorite, and greywacke. 

 

NF EN ISO 28692 (Alga, Growth Inhibition Test) using the freshwater alga Pseudokirchneriella subcapitata:

In an acute toxicity test according to NF EN ISO 28692, leachate (L/S 10/1) of ferrous slag yielded the following results:

ABS (2 samples): For both slags, the 72 h-NOEC is >= 90 g/L (nominal, highest concentration tested, LECES 1999)

EAF C: 72 h-NOEC = 11 g/L (nominal) (LECES 1999)

EAF S: 72 h-NOEC = 18 g/L (nominal) (LECES 1999)

 

Fertilizer studies

To elucidate the possibility to use steelmaking slags as fertilizers for marine phytoplankton, solubilization of elements of nutritional value, N, P, Si and Fe was examined in artificial saltwater. Slags, steelmaking, would sustain marine phytoplankton growth (Futatsuka et al. 2003).

The same results were obtained in another study of the same year. Fertilization with slags would especially favour diatoms like Skeletonema costatum (Nakamura and Taniguchi 2003)

 

Field studies

The colonization of EAF C and natural rock fields on banks of theriver by sessile algal populations was examined qualitatively and quantitatively in field experiments by microscopic determination of algal species and counting of cells. EAF C and natural rock (diabase) used as a stone material for river bank protection is equally well colonized by algae. Differences in the density of the total algal populations were not statistically significant. On EAF C there was a significant increase in the number of two diatomeous species, whereas no significant differences occurred for green or blue-green algae. As there were approximately 30 groups of algae examined, and the effect was only significant for part of the observation period, it is unlikely, that this effect has any environmental relevance. No toxic effect was exerted by EAF C (Universitaet Hamburg 1996).

The colonization of EAF C and natural rock plates exposed to theriver by sessile algal populations was examined qualitatively and quantitatively in field experiments by microscopic determination of algal species and counting of cells. EAF C and natural rocks (granite, diabase, basalt) are equally well colonized by algae. Differences in the density of the total algal populations were not statistically significant after the observation period of 8 weeks. There were no relevant differences in the species composition of the algal populations on basalt, granite, and EAF C. No toxic effect is exerted by EAF C in the environment (Universitaet Hamburg 1996).

The elucidate the ecological effects of slag as a substrate for growth of marine algae, basic steelmaking slags were stabilized by carbon dioxide uptake (formation of carbonate with free calcium oxide/calcium hydroxide) in the form of blocks (1m x 1m x 1 m). In November 2001, 5 slag blocks and 5 concrete blocks of the same size were placed close to Ecklonia cava beds (“marine forests”) in a water depth of 7 m around the coastal area of Jogashima at the mouth of Tokyo Bay. Scuba-diving observations were continued until April 2006. In July 2005, 2 blocks each were taken from the water for detailed analysis of plant and animal populations. In the field, a large number of seaweed and animal species were observed on the slag blocks and on concrete blocks. The number of young individuals of Ecklonia cava was higher on concrete due to slower speed of succession. All other parameters examined, e.g. the speed and variety of succession, the plant length and the wet weight of Ecklonia cava were greater on slag blocks than on concrete blocks, suggesting that stabilized steelmaking slag is an excellent substrate for growth of algae (Oyamada et al. 2008).

To examine the ecological behaviour of slag stones in the environment, several slag stones were exposed to environmental waters in a channel in. Within 5 weeks of exposure to the channel water, the slag stones were covered with dense growth of green algae. Due to the algal cover, the slag stones were almost indistinguishable from stones of stone fields exposed to the channel water for years at the same site, substantiating that slag stones are an excellent substrate for algal growth (Kils 1992).