Dissolved organic carbon reduces the toxicity of aluminum to three tropical freshwater organisms

Abstract

The influence of dissolved organic carbon (DOC) on the toxicity of aluminum (Al) at pH 5 (relevant to acid mine drainage conditions), to the tropical green hydra (Hydra viridissima), green alga (Chlorella sp.), and cladoceran (Moinodaphnia macleayi) was assessed. Two DOC sources, a natural in situ DOC in soft billabong water (SBW) and Suwannee River fulvic acid (SRFA) standard, were compared. The order of sensitivity of the test organisms to dissolved Al (0.1 µm fraction) was Hydra viridissima > Moinodaphnia macleayi > Chlorella sp. with DOC reducing dissolved Al toxicity most for Hydra viridissima. However, colloidal or precipitated Al may contribute indirectly to the toxicity for M. macleayi and Chlorella sp. The toxicity of dissolved Al was up to six times lower in test waters containing 10 mg L(-1) DOC (in the form of SRFA), relative to toxicity observed at 1 mg L(-1) DOC. In contrast, the toxicity of Al was up to two times lower in SBW containing 10 mg L(-1) DOC, relative to water containing 1 mg L(-1) DOC. The increased ability of SRFA in reducing Al toxicity was linked to its greater affinity for complexing Al compared with the in situ DOC. This has important implications for studies that use commercial standards of humic substances to predict Al toxicity in local environments. Speciation modeling demonstrated that Al(3+) and AlOH(2+) provided a strong relationship with toxicity. An empirical relationship is provided for each organism that can be used to predict Al toxicity at a given Al and DOC concentration.

Acute and chronic toxicity of aluminum to a unionid mussel (Lampsilis siliquoidea) and an amphipod (Hyalella azteca) in water‐only exposures

“…Numerous studies have demonstrated that Al toxicity to aquatic organisms is influenced not only by pH and hardness but also by other water characteristics, including DOC; temperature; alkalinity; concentrations of major anions, cations, and sulfide; Al speciation; polymerization; and the presence of competing ligands and complexing agents [3][4][5][6][7][8][9][37][38][39][40][41][42]. These relationships form the basis of a freshwater Al biotic ligand model that was recently developed to enable mechanistic modeling of Al bioavailability and chronic toxicity as a function of water quality variables [8].…”

Derivation of a water quality guideline for aluminium in marine waters

“…The 72-h IC10 concurred with that derived in the present study (Table 1) using the temperate strain of the same species. Information on aluminium speciation and effects on algae in freshwaters [22,23] is more readily available but has focused on situations of lower pH where aluminium speciation is dominated by the monomeric trivalent forms (Al 3þ ), hydroxy forms (Al(OH) 2þ , Al(OH) 2 þ ), and organic complexes. These forms are not comparable with aluminium speciation and toxicity at the pH, DOC, and ionic composition of seawater.…”

Evaluating the effects of pH, hardness, and dissolved organic carbon on the toxicity of aluminum to freshwater aquatic organisms under circumneutral conditions

“…Furthermore, the potential effects of hardness or dissolved organic carbon (DOC) complexation on Al toxicity were not considered even though they exert significant effects on the toxicity of most metals [2][3][4]. Although the effects of hardness cations and DOC on Al toxicity are well understood under acidic pH conditions [5,6], their effects have not yet been rigorously evaluated under more circumneutral conditions.…”

“…Furthermore, the potential effects of hardness or dissolved organic carbon (DOC) complexation on Al toxicity were not considered even though they exert significant effects on the toxicity of most metals [2][3][4]. Although the effects of hardness cations and DOC on Al toxicity are well understood under acidic pH conditions [5,6], their effects have not yet been rigorously evaluated under more circumneutral conditions. The toxicity of Al to freshwater organisms occurs via 2 primary mechanisms: 1) iono-regulatory disturbance from exposure to the dissolved monomeric species that predominate under more acidic pH (e.g., free Al 3þ or newly formed amorphous Al(OH) 3 ); and 2) respiratory disturbance from the accumulation of precipitated forms of Al that predominate at circumneutral pH [5,7].…”