# Could Acidified Environments Intensity Illicit Drug Effects on the Reproduction of Marine Mussets?
## 1 Introduction  
Mauna Loa observatory [1] observed a peak in atmospheric CO\({}_{2}\) in May 2021 (monthly average 419 ppm). This and other greenhouse gases are causing global environmental change [2]. However, the exchange of CO\({}_{2}\) between the atmosphere and the hydrosphere promotes ocean acidification (OA) by decreasing the pH of average surface seawater [3]. We estimate a decrease of 0.67 units of pH in seawater by 2300 with respect to preindustrial pH levels [4].  
The increase in CO\({}_{2}\) atmospheric burden promotes the increasing oceanic uptake, so that oceans experience both physical and biogeochemical changes: surface and deep water warming, reduced subsurface oxygen, and a reduction in CaCO\({}_{3}\) saturation levels and pH [5]. The oceanic biogeochemical dynamics are increasingly relevant in the assessment of the ecosystem health, climate impacts, mitigation strategies, and planetary sustainability [4]. Some previous studies have indicated that OA over-calcifies marine organisms [6, 7, 8, 9], marine bacteria [10, 11, 12], amphipods [13], macro-algae [14, 15], or macro-fauna [16, 17].  
OA interacts with local stressors, such as xenobiotics and other emerging compounds. Nevertheless, nowadays, these interactions between OA, environmental changes, and contaminants require greater scientific knowledge [18]. The seawater pH decrease caused by increasing CO\({}_{2}\) can modify the speciation of compounds, due to largely dependent elements' speciation on physicochemical parameters (salinity, pH, potential redox) [19, 20],and therefore their bioavailability for organisms [21]. Previous studies have shown the effect of OA on the speciation of metals [7; 20; 22]; however, this is still poorly investigated for contaminants acting as emerging compounds, and as pharmaceuticals.  
The occurrence of pharmaceuticals and personal care products (PPCPs) in the environment is increasingly recognized as an important issue [23; 24; 25; 26]. This includes illicit drugs; emerging pollutants are also considered [27; 28]. Pharmaceuticals and illicit drugs, once ingested, are partially metabolized due to their particular solubility, and enter the sewage stream [29], but the inefficient or incomplete treatment causes marine pollution. Once in the environment, illicit drugs promote adverse effects in non-target organisms, as demonstrated by some studies with cocaine byproducts [30; 31; 32; 33; 34]. The marine mussels _Perna perna_ exposed to 0.5 and 5 ng L\({}^{-1}\) exhibited cytotoxicity linked to the instability of the lysosomal membrane [31], biomarker responses (EROD, DBF, GST, GPx) [23], and how detoxification, oxidative stress, and cytogenotoxicity are caused [32]. However, CC metabolites [33] also promoted sublethal effects in _D. polymorpha_. Additionally, crustaceans exposed to CC showed an increase in motility [23]. CC effects in mammals, such as mice, display genotoxicity and mutagenicity induced by acute crack cocaine exposure [34]. However, the effects in molluss under acidified environments with illicit drug presence required further research.  
Understanding factors affecting the survivorship and growth of juvenile mussels through vulnerable early life stages is critical both for aquaculture efforts and ecology equilibrium. This work aims to assess how acidification can trigger enhanced toxicity of illicit drugs to non-target marine organisms due to the combined effects of crack cocaine (CC) and low pH (from 8.3 to 7.0 pH values) on the reproduction of the marine mussel _Perna perna_. To achieve this, two acidification methodologies were applied (HCl and CO\({}_{2}\) injection). Additionally, the toxicity test endpoints for mussels were survival, fertility, and embryo-larval development.